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Chapter 1 Prerequisites

1.1 Real Numbers: Algebra Essentials

Learning Objectives

In this section, you will:

  • Classify a real number as a natural, whole, integer, rational, or irrational number.
  • Perform calculations using order of operations.
  • Use the following properties of real numbers: commutative, associative, distributive, inverse, and identity.
  • Evaluate algebraic expressions.
  • Simplify algebraic expressions.

It is often said that mathematics is the language of science. If this is true, then an essential part of the language of mathematics is numbers. The earliest use of numbers occurred 100 centuries ago in the Middle East to count, or enumerate, items. Farmers, cattlemen, and tradesmen used tokens, stones, or markers to signify a single quantity—a sheaf of grain, a head of livestock, or a fixed length of cloth, for example. Doing so made commerce possible, leading to improved communications and the spread of civilization.

Three to four thousand years ago, Egyptians introduced fractions. They first used them to show reciprocals. Later, they used them to represent the amount when a quantity was divided into equal parts.

But what if there were no cattle to trade or an entire crop of grain was lost in a flood? How could someone indicate the existence of nothing? From earliest times, people had thought of a “base state” while counting and used various symbols to represent this null condition. However, it was not until about the fifth century A.D. in India that zero was added to the number system and used as a numeral in calculations.

Clearly, there was also a need for numbers to represent loss or debt. In India, in the seventh century A.D., negative numbers were used as solutions to mathematical equations and commercial debts. The opposites of the counting numbers expanded the number system even further.

Because of the evolution of the number system, we can now perform complex calculations using these and other categories of real numbers. In this section, we will explore sets of numbers, calculations with different kinds of numbers, and the use of numbers in expressions.

Classifying a Real Number

The numbers we use for counting or enumerating items are the natural numbers: 1, 2, 3, 4, 5, and so on. We describe them in set notation as{1,2,3,...}{1,2,3,...}, where the ellipsis (…) indicates that the numbers continue to infinity. The natural numbers are, of course, also called the counting numbers. Any time we enumerate the members of a team, count the coins in a collection, or tally the trees in a grove, we are using the set of natural numbers. The set of whole numbers is the set of natural numbers plus zero:{0,1,2,3,...}.{0,1,2,3,...}.

The set of integers adds the opposites of the natural numbers to the set of whole numbers:{...,3,2,1,0,1,2,3,...}.{...,3,2,1,0,1,2,3,...}. It is useful to note that the set of integers is made up of three distinct subsets: negative integers, zero, and positive integers. In this sense, the positive integers are just the natural numbers. Another way to think about it is that the natural numbers are a subset of the integers.

negative integers,3,2,1,zero0,positive integers1,2,3,negative integers,3,2,1,zero0,positive integers1,2,3,

 

negative integers,3,2,1,zero0,positive integers1,2,3,negative integers,3,2,1,zero0,positive integers1,2,3,

The set of rational numbers is written as{mn|m and n are integers and n0}.{mn|m and n are integers and n0}.Notice from the definition that rational numbers are fractions (or quotients) containing integers in both the numerator and the denominator, and the denominator is never 0. We can also see that every natural number, whole number, and integer is a rational number with a denominator of 1.

Because they are fractions, any rational number can also be expressed in decimal form. Any rational number can be represented as either:

  1. a terminating decimal:158=1.875,158=1.875, or
  2. a repeating decimal:411=0.36363636=0.¯36411=0.36363636=0.¯¯¯¯¯¯36

We use a line drawn over the repeating block of numbers instead of writing the group multiple times.

Writing Integers as Rational Numbers

Write each of the following as a rational number.

  1. 7
  2. 0
  3. –8
Show Solution

Write a fraction with the integer in the numerator and 1 in the denominator.

  1. 7=717=71
  2. 0=010=01
  3. 8=818=81

Try It

Write each of the following as a rational number.

  1. 11
  2. 3
  3. –4
Show Solution
  1. 111111
  2. 3131
  3. 4141

Identifying Rational Numbers

Write each of the following rational numbers as either a terminating or repeating decimal.

  1. 5757
  2. 155155
  3. 13251325
Show Solution

Write each fraction as a decimal by dividing the numerator by the denominator.

  1. 57=0.———714285,57=0.———714285, a repeating decimal
  2. 155=3155=3(or 3.0), a terminating decimal
  3. 1325=0.52,1325=0.52, a terminating decimal

Try It

Write each of the following rational numbers as either a terminating or repeating decimal.

  1. 68176817
  2. 813813
  3. 17201720
Show Solution
  1. 4 (or 4.0), terminating;
  2. 0.¯615384,0.¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯615384,repeating;
  3. –0.85, terminating

Irrational Numbers

At some point in the ancient past, someone discovered that not all numbers are rational numbers. A builder, for instance, may have found that the diagonal of a square with unit sides was not 2 or even32,32,but was something else. Or a garment maker might have observed that the ratio of the circumference to the diameter of a roll of cloth was a little bit more than 3, but still not a rational number. Such numbers are said to be irrational because they cannot be written as fractions. These numbers make up the set of irrational numbers. Irrational numbers cannot be expressed as a fraction of two integers. It is impossible to describe this set of numbers by a single rule except to say that a number is irrational if it is not rational. So we write this as shown.

{h|h is not a rational number}{h|h is not a rational number}

Differentiating Rational and Irrational Numbers

Determine whether each of the following numbers is rational or irrational. If it is rational, determine whether it is a terminating or repeating decimal.

  1. 2525
  2. 339339
  3. 1111
  4. 17341734
  5. 0.30330333033330.3033033303333
Show Solution
  1. 25:25:This can be simplified as25=5.25=5.Therefore,2525is rational.
  2. 339:339:Because it is a fraction,339339is a rational number. Next, simplify and divide.
    339=11¯)33¯)93=113=3.¯6339=11¯¯¯¯¯¯¯¯)33¯¯¯¯¯)93=113=3.¯¯¯6

    So,339339is rational and a repeating decimal.

  3. 11:11:This cannot be simplified any further. Therefore,1111is an irrational number.
  4. 1734:1734:Because it is a fraction,17341734is a rational number. Simplify and divide.
    1734=1¯)17¯)342=12=0.51734=1¯¯¯¯¯¯¯¯)17¯¯¯¯¯¯¯¯)342=12=0.5

    So,17341734is rational and a terminating decimal.

  5. 0.30330333033330.3033033303333is not a terminating decimal. Also note that there is no repeating pattern because the group of 3s increases each time. Therefore it is neither a terminating nor a repeating decimal and, hence, not a rational number. It is an irrational number.

Try It

Determine whether each of the following numbers is rational or irrational. If it is rational, determine whether it is a terminating or repeating decimal.

  1. 777777
  2. 8181
  3. 4.270270027000274.27027002700027
  4. 91139113
  5. 3939
Show Solution
  1. rational and repeating;
  2. rational and terminating;
  3. irrational;
  4. rational and repeating;
  5. irrational

Real Numbers

Given any number n, we know that n is either rational or irrational. It cannot be both. The sets of rational and irrational numbers together make up the set of real numbers. As we saw with integers, the real numbers can be divided into three subsets: negative real numbers, zero, and positive real numbers. Each subset includes fractions, decimals, and irrational numbers according to their algebraic sign (+ or –). Zero is considered neither positive nor negative.

The real numbers can be visualized on a horizontal number line with an arbitrary point chosen as 0, with negative numbers to the left of 0 and positive numbers to the right of 0. A fixed unit distance is then used to mark off each integer (or other basic value) on either side of 0. Any real number corresponds to a unique position on the number line. The converse is also true: Each location on the number line corresponds to exactly one real number. This is known as a one-to-one correspondence. We refer to this as the real number line, as shown in (Figure 1).

 

A number line that is marked from negative five to five.
Figure 1. The real number line

Classifying Real Numbers

Classify each number as either positive or negative and as either rational or irrational. Does the number lie to the left or the right of 0 on the number line?

  1. 103103
  2. 55
  3. 289289
  4. 6π6π
  5. 0.6153846153840.615384615384
Show Solution
  1. 103103is negative and rational. It lies to the left of 0 on the number line.
  2. 55is positive and irrational. It lies to the right of 0.
  3. 289=172=17289=172=17is negative and rational. It lies to the left of 0.
  4. 6π6πis negative and irrational. It lies to the left of 0.
  5. 0.6153846153840.615384615384is a repeating decimal so it is rational and positive. It lies to the right of 0.

Try It

Classify each number as either positive or negative and as either rational or irrational. Does the number lie to the left or the right of 0 on the number line?

  1. 7373
  2. 11.41141141111.411411411
  3. 47194719
  4. 5252
  5. 6.2107356.210735
Show Solution
  1. positive, irrational; right
  2. negative, rational; left
  3. positive, rational; right
  4. negative, irrational; left
  5. positive, rational; right

Sets of Numbers as Subsets

Beginning with the natural numbers, we have expanded each set to form a larger set, meaning that there is a subset relationship between the sets of numbers we have encountered so far. These relationships become more obvious when seen as a diagram, such as Figure 2.

A large box labeled: Real Numbers encloses five circles. Four of these circles enclose each other and the other is separate from the rest. The innermost circle contains: 1, 2, 3… N. The circle enclosing that circle contains: 0 W. The circle enclosing that circle contains: …, -3, -2, -1 I. The outermost circle contains: m/n, n not equal to zero Q. The separate circle contains: pi, square root of two, etc Q´.
Figure 2. Sets of numbers N: the set of natural numbers W: the set of whole numbers I: the set of integers Q: the set of rational numbers Q´: the set of irrational numbers

Sets of Numbers

The set of natural numbers includes the numbers used for counting:{1,2,3,...}.{1,2,3,...}.

The set of whole numbers is the set of natural numbers plus zero:{0,1,2,3,...}.{0,1,2,3,...}.

The set of integers adds the negative natural numbers to the set of whole numbers:{...,3,2,1,0,1,2,3,...}.{...,3,2,1,0,1,2,3,...}.

The set of rational numbers includes fractions written as{mn|m and n are integers and n0}.{mn|m and n are integers and n0}.

The set of irrational numbers is the set of numbers that are not rational, are nonrepeating, and are nonterminating:{h|h is not a rational number}.{h|h is not a rational number}.

Differentiating the Sets of Numbers

Classify each number as being a natural number (N), whole number (W), integer (I), rational number (Q), and/or irrational number (Q′).

  1. 3636
  2. 8383
  3. 7373
  4. 66
  5. 3.21211211123.2121121112
Show Solution
N W I Q Q′
a.36=636=6 X X X X
b.83=2.¯683=2.¯¯¯6 X
c.7373 X
d. –6 X X
e. 3.2121121112… X

Try It

Classify each number as being a natural number (N), whole number (W), integer (I), rational number (Q), and/or irrational number (Q′).

  1. 357357
  2. 00
  3. 169169
  4. 2424
  5. 4.7637637634.763763763
Show Solution
N W I Q Q’
a.357357 X X
b. 0 X X X
c.169169 X X X X
d.2424 X
e. 4.763763763… X

Performing Calculations Using the Order of Operations

When we multiply a number by itself, we square it or raise it to a power of 2. For example,42=44=16.42=44=16.We can raise any number to any power. In general, the exponential notationananmeans that the number or variableaais used as a factornntimes.

an=n factorsaaaaan=n factorsaaaa

In this notation,ananis read as the nth power ofa,a,whereaais called the base andnnis called the exponent. A term in exponential notation may be part of a mathematical expression, which is a combination of numbers and operations. For example,24+6234224+62342is a mathematical expression.

To evaluate a mathematical expression, we perform the various operations. However, we do not perform them in any random order. We use the order of operations. This is a sequence of rules for evaluating such expressions.

Recall that in mathematics we use parentheses ( ), brackets [ ], and braces { } to group numbers and expressions so that anything appearing within the symbols is treated as a unit. Additionally, fraction bars, radicals, and absolute value bars are treated as grouping symbols. When evaluating a mathematical expression, begin by simplifying expressions within grouping symbols.

The next step is to address any exponents or radicals. Afterward, perform multiplication and division from left to right and finally addition and subtraction from left to right.

Let’s take a look at the expression provided.

24+6234224+62342

There are no grouping symbols, so we move on to exponents or radicals. The number 4 is raised to a power of 2, so simplify4242as 16.

24+6234224+6231624+6234224+62316

Next, perform multiplication or division, left to right.

24+6231624+41624+6231624+416

Lastly, perform addition or subtraction, left to right.

24+416 2816 1224+416 2816 12

Therefore,24+62342=12.24+62342=12.

For some complicated expressions, several passes through the order of operations will be needed. For instance, there may be a radical expression inside parentheses that must be simplified before the parentheses are evaluated. Following the order of operations ensures that anyone simplifying the same mathematical expression will get the same result.

Order of Operations

Operations in mathematical expressions must be evaluated in a systematic order, which can be simplified using the acronym PEMDAS:

P(arentheses)

E(xponents)

M(ultiplication) and D(ivision)

A(ddition) and S(ubtraction)

How To

Given a mathematical expression, simplify it using the order of operations.

  1. Simplify any expressions within grouping symbols.
  2. Simplify any expressions containing exponents or radicals.
  3. Perform any multiplication and division in order, from left to right.
  4. Perform any addition and subtraction in order, from left to right.

Using the Order of Operations

Use the order of operations to evaluate each of the following expressions.

  1. (32)24(6+2)(32)24(6+2)
  2. 52471125247112
  3. 6|58|+3(41)6|58|+3(41)
  4. 1432253214322532
  5. 7(53)2[(63)42]+1
Show Solution
  1. (3 * 2)2 – 4 (6 + 2)
    = 62 – 4(8) Simplify parentheses
    = 36 – 4(8) Simplify exponent
    = 36 – 32 Simplify multiplication
    = 4 Simplify subtraction
  2. Note that in the first step, the radical is treated as a grouping symbol, like parentheses. Also, in the third step, the fraction bar is considered a grouping symbol,  so the numerator is considered to be grouped.
  3. 6 – |5 – 8| + 3 (4 – 1)
    6 – |-3| + 3 (3) Simplify inside grouping symbols
    = 6 – 3 + 3 (3) Simplify absolute value
    = 6 – 3 + 9 Simplify multiplication
    = 3 + 9 Simplify subtraction
    = 12 Simplify addition
  4. In this example, the fraction bar separates the numerator and denominator, which we simplify separately until the last step.
  5. 7 (5 * 3) – 2 [(6 – 3) – 4+ 1 = 7 (15) – 2 [(3) – 4] + 1 Simplify inside parentheses
    = 7 (15) – 2 (3 – 16 ) + 1 Simplify exponent
    =  7 (15) – 2 (-13) + 1 Subtract
    = 105 + 26 + 1 Multiply
    = 132 Add

Try It

Use the order of operations to evaluate each of the following expressions.

  1. 5242+7(54)2
  2. 1+758496
  3. |1.84.3|+0.415+10
  4. 12[53272]+1392
  5. [(38)24](38)
Show Solution
  1. 10
  2. 2
  3. 4.5
  4. 25
  5. 26

Using Properties of Real Numbers

For some activities we perform, the order of certain operations does not matter, but the order of other operations does. For example, it does not make a difference if we put on the right shoe before the left or vice-versa. However, it does matter whether we put on shoes or socks first. The same thing is true for operations in mathematics.

Commutative Properties

The commutative property of addition states that numbers may be added in any order without affecting the sum.

a+b=b+a

We can better see this relationship when using real numbers.

(2)+7=5and7+(2)=5

Similarly, the commutative property of multiplication states that numbers may be multiplied in any order without affecting the product.

ab=ba

Again, consider an example with real numbers.

(11)(4)=44and(4)(11)=44

It is important to note that neither subtraction nor division is commutative. For example,175is not the same as517.Similarly,20÷55÷20.

Associative Properties

The associative property of multiplication tells us that it does not matter how we group numbers when multiplying. We can move the grouping symbols to make the calculation easier, and the product remains the same.

a(bc)=(ab)c

Consider this example.

(34)5=60and3(45)=60

The associative property of addition tells us that numbers may be grouped differently without affecting the sum.

a+(b+c)=(a+b)+c

This property can be especially helpful when dealing with negative integers. Consider this example.

[15+(9)]+23=29and15+[(9)+23]=29

Are subtraction and division associative? Review these examples.

8(315)?=(83)1564÷(8÷4)?=(64÷8)÷48(12)=515 64÷2?= 8÷420 2010 322

As we can see, neither subtraction nor division is associative.

Distributive Property

The distributive property states that the product of a factor times a sum is the sum of the factor times each term in the sum.

a(b+c)=ab+ac

This property combines both addition and multiplication (and is the only property to do so). Let us consider an example.

The number four is separated by a multiplication symbol from a bracketed expression reading: twelve plus negative seven. Arrows extend from the four pointing to the twelve and negative seven separately. This expression equals four times twelve plus four times negative seven. Under this line the expression reads forty eight plus negative twenty eight. Under this line the expression reads twenty as the answer.

Note that 4 is outside the grouping symbols, so we distribute the 4 by multiplying it by 12, multiplying it by –7, and adding the products.

To be more precise when describing this property, we say that multiplication distributes over addition. The reverse is not true, as we can see in this example.

6+(35)?=(6+3)(6+5)6+(15)?=(9)(11)21 99

A special case of the distributive property occurs when a sum of terms is subtracted.

ab=a+(b)

For example, consider the difference12(5+3).We can rewrite the difference of the two terms 12 and(5+3)by turning the subtraction expression into addition of the opposite. So instead of subtracting(5+3),we add the opposite.

12+(1)(5+3)

Now, distribute1and simplify the result.

12(5+3)=12+(1)(5+3)=12+[(1)5+(1)3]=12+(8)=4

This seems like a lot of trouble for a simple sum, but it illustrates a powerful result that will be useful once we introduce algebraic terms. To subtract a sum of terms, change the sign of each term and add the results. With this in mind, we can rewrite the last example.

12(5+3)=12+(53)=12+(8)=4

Identity Properties

The identity property of addition states that there is a unique number, called the additive identity (0) that, when added to a number, results in the original number.

a+0=a

The identity property of multiplication states that there is a unique number, called the multiplicative identity (1) that, when multiplied by a number, results in the original number.

a1=a

For example, we have(6)+0=6and231=23.There are no exceptions for these properties; they work for every real number, including 0 and 1.

Inverse Properties

The inverse property of addition states that for every real number a, there is a unique number, called the additive inverse (or opposite), denoted−a, that, when added to the original number, results in the additive identity, 0.

a+(a)=0

For example, ifa=8,the additive inverse is 8, since(8)+8=0.

The inverse property of multiplication holds for all real numbers except 0 because the reciprocal of 0 is not defined. The property states that for every real number a, there is a unique number, called the multiplicative inverse (or reciprocal), denoted1a, that, when multiplied by the original number, results in the multiplicative identity, 1.

a1a=1

For example, ifa=23, the reciprocal, denoted1a, is32
because

a1a=(23)(32)=1

Properties of Real Numbers

The following properties hold for real numbers a, b, and c.

Addition Multiplication
Commutative Property a+b=b+a ab=ba
Associative Property a+(b+c)=(a+b)+c a(bc)=(ab)c
Distributive Property a(b+c)=ab+ac
Identity Property There exists a unique real number called the additive identity, 0, such that, for any real number a
a+0=a
There exists a unique real number called the multiplicative identity, 1, such that, for any real number a
a1=a
Inverse Property Every real number a has an additive inverse, or opposite, denoted –a, such that
a+(a)=0
Every nonzero real number a has a multiplicative inverse, or reciprocal, denoted1a,such that
a(1a)=1

Using Properties of Real Numbers

Use the properties of real numbers to rewrite and simplify each expression. State which properties apply.

  1. 36+34
  2. (5+8)+(8)
  3. 6(15+9)
  4. 47(2374)
  5. 100[0.75+(2.38)]
Show Solution
  1. a.  3 * 6 + 3 * 4 = 3 * (6 + 4) Distributive property
    = 3 * 10 Simplify
    = 30 Simplify
    b.  (5 + 8) + (-8) = 5 + [8 + (-8)] Associative property of addition
    = 5 + 0 Inverse property of addition
    = 5 Identity property of addition
    c.  6 – (15  + 9) = 6 + [(-15) + (-9)] Distributive property
    = 6 +  (-24) Simplify
    = -18 Simplify
    d.47(23*74)

     

    = 47(74*23) Commutative property of multiplication
    = (4774) 23 Associative property of multiplication
    = 1 * 23 Inverse property of multiplication
    = 23 Identity property of multiplication
    e. 100 [0.75 + (-2.38)] = 100 * 0.75 + 100 * (-2.38) Distributive property
    = 75 + (2.38) Simply
    = -163 Simplify

Use the properties of real numbers to rewrite and simplify each expression. State which properties apply.

  1. (235)[11(523)]
  2. 5(6.2+0.4)
  3. 18(715)
  4. 1718+[49+(1718)]
  5. 6(3)+63
Show Solution
  1. 11, commutative property of multiplication, associative property of multiplication, inverse property of multiplication, identity property of multiplication;
  2. 33, distributive property;
  3. 26, distributive property;
  4. 49, commutative property of addition, associative property of addition, inverse property of addition, identity property of addition;
  5. 0, distributive property, inverse property of addition, identity property of addition

Evaluating Algebraic Expressions

So far, the mathematical expressions we have seen have involved real numbers only. In mathematics, we may see expressions such asx+5,43πr3, or2m3n2.In the expressionx+5, 5 is called a constant because it does not vary, and x is called a variable because it does. (In naming the variable, ignore any exponents or radicals containing the variable.) An algebraic expression is a collection of constants and variables joined together by the algebraic operations of addition, subtraction, multiplication, and division.

We have already seen some real number examples of exponential notation, a shorthand method of writing products of the same factor. When variables are used, the constants and variables are treated the same way.

(3)5=(3)(3)(3)(3)(3)x5=xxxxx(27)3=(27)(27)(27) (yz)3=(yz)(yz)(yz)

In each case, the exponent tells us how many factors of the base to use, whether the base consists of constants or variables.

Any variable in an algebraic expression may take on or be assigned different values. When that happens, the value of the algebraic expression changes. To evaluate an algebraic expression means to determine the value of the expression for a given value of each variable in the expression. Replace each variable in the expression with the given value, then simplify the resulting expression using the order of operations. If the algebraic expression contains more than one variable, replace each variable with its assigned value and simplify the expression as before.

Describing Algebraic Expressions

List the constants and variables for each algebraic expression.

  1. x + 5
  2. 43πr3
  3. 2m3n2
Show Solution
Constants Variables
a. x + 5 5 x
b.43πr3 43,π r
c.2m3n2 2 m,n

Try It

List the constants and variables for each algebraic expression.

  1. 2πr(r+h)
  2. 2(L+W)
  3. 4y3+y
Show Solution
Constants Variables
a.2πr(r+h) 2,π r,h
b. 2(L+W) 2 L,W
c.4y3+y 4 y

Evaluating an Algebraic Expression at Different Values

Evaluate the expression2x7for each value for x.

  1. x=0
  2. x=1
  3. x=12
  4. x=4
Show Solution
  1. Substitute 0 forx.
    2x7=2(0)7=07=7
  2. Substitute 1 forx.
    2x7=2(1)7=27=5
  3. Substitute12forx.
    2x7=2(12)7=17=6
  4. Substitute4forx.
    2x7=2(4)7=87=15

Try It

Evaluate the expression113yfor each value for y.

  1. y=2
  2. y=0
  3. y=23
  4. y=5
Show Solution
  1. 5
  2. 11
  3. 9
  4. 26

Evaluating Algebraic Expressions

Evaluate each expression for the given values.

  1. x+5forx=5
  2. t2t1fort=10
  3. 43πr3forr=5
  4. a+ab+bfora=11,b=8
  5. 2m3n2form=2,n=3
Show Solution
  1. Substitute5forx.
    x+5=(5)+5=0
  2. Substitute 10 fort.
    t2t1=(10)2(10)1=10201=1019
  3. Substitute 5 forr.
    43πr3=43π(5)3=43π(125)=5003π
  4. Substitute 11 foraand –8 forb.
    a+ab+b=(11)+(11)(8)+(8)=11888=85
  5. Substitute 2 formand 3 forn.
    2m3n2=2(2)3(3)2=2(8)(9)=144=12

Try It

Evaluate each expression for the given values.

  1. y+3y3fory=5
  2. 72tfort=2
  3. 13πr2forr=11
  4. (p2q)3forp=2,q=3
  5. 4(mn)5(nm)form=23,n=13
Show Solution
  1. 4
  2. 11
  3. 1213π
  4. 1728
  5. 3

Formulas

An equation is a mathematical statement indicating that two expressions are equal. The expressions can be numerical or algebraic. The equation is not inherently true or false, but only a proposition. The values that make the equation true, the solutions, are found using the properties of real numbers and other results. For example, the equation2x+1=7has the unique solution of 3 because when we substitute 3 forxin the equation, we obtain the true statement 2(3)+1=7.

A formula is an equation expressing a relationship between constant and variable quantities. Very often, the equation is a means of finding the value of one quantity (often a single variable) in terms of another or other quantities. One of the most common examples is the formula for finding the areaAof a circle in terms of the radiusrof the circle:A=πr2.For any value ofr, the areaAcan be found by evaluating the expressionπr2.

Using a Formula

A right circular cylinder with radiusrand heighthhas the surface areaS(in square units) given by the formulaS=2πr(r+h).See Figure 3. Find the surface area of a cylinder with radius 6 in. and height 9 in. Leave the answer in terms ofπ.

A right circular cylinder with an arrow extending from the center of the top circle outward to the edge, labeled: r. Another arrow beside the image going from top to bottom, labeled: h.
Figure 3 Right Circular Cylinder
Show Solution

Evaluate the expression2πr(r+h)forr=6andh=9.

S=2πr(r+h)=2π(6)[(6)+(9)]=2π(6)(15)=180π

The surface area is180πsquare inches.

Try It

A photograph with length L and width W is placed in a matte of width 8 centimeters (cm). The area of the matte (in square centimeters, or cm2) is found to beA=(L+16)(W+16)LW.See Figure 4. Find the area of a matte for a photograph with length 32 cm and width 24 cm.

/ An art frame with a piece of artwork in the center. The frame has a width of 8 centimeters. The artwork itself has a length of 32 centimeters and a width of 24 centimeters.
Figure 4
Show Solution

Given that L=32 and W=24, plug the numbers into the formula A=(L+16)(W+16)LW.

A=(32+16)(24+16)3224.

A=(48)(40)512.

1,152 cm2

Simplifying Algebraic Expressions

Sometimes we can simplify an algebraic expression to make it easier to evaluate or to use in some other way. To do so, we use the properties of real numbers. We can use the same properties in formulas because they contain algebraic expressions.

Simplifying Algebraic Expressions

Simplify each algebraic expression.

  1. 3x2y+x3y7
  2. 2r5(3r)+4
  3. (4t54s)(23t+2s)
  4. 2mn5m+3mn+n
Show Solution
a. 3x -2y + x – 3y – 7 = 3x + x – 2y – 3y – 7 Commutative property of addition
= 4x – 5y – 7 Simplify
b.  2r – 5 (3 – r) + 4 = 2r – 15 + 5r + 4 Distributive property
= 2r + 5r – 15 + 4 Commutative property of addition
= 7r – 11 Simplify
c. (4t – 54s) – (23t + 2s) = 4t – 54s – 23s – 2s Distributive property
=  4t – 23t – 54s – 2s Commutative property of addition
d.  2mn  – 5m +3mn + n = 103t – 134s Simplify
= 2mn +3mn -5m + n Commutative property of addition
= 5mn – 5m + n Simplify

Try It

Simplify each algebraic expression.

  1. 23y2(43y+z)
  2. 5t23t+1
  3. 4p(q1)+q(1p)
  4. 9r(s+2r)+(6s)
Show Solution
  1. 2y2z or 2(y+z);
  2. 2t1;
  3. 3pq4p+q;
  4. 7r2s+6

Simplifying a Formula

A rectangle with lengthLand widthWhas a perimeterPgiven byP=L+W+L+W.Simplify this expression.

Show Solution
P=L+W+L+WP=L+L+W+WCommutative property of additionP=2L+2WSimplifyP=2(L+W)Distributive property

Try It

If the amountPis deposited into an account paying simple interestrfor timet, the total value of the depositAis given byA=P+Prt.Simplify the expression. (This formula will be explored in more detail later in the course.)

Show Solution

A=P(1+rt)

 

Key Concepts

  • Rational numbers may be written as fractions or terminating or repeating decimals.
  • Determine whether a number is rational or irrational by writing it as a decimal.
  • The rational numbers and irrational numbers make up the set of real numbers. A number can be classified as natural, whole, integer, rational, or irrational.
  • The order of operations is used to evaluate expressions.
  • The real numbers under the operations of addition and multiplication obey basic rules, known as the properties of real numbers. These are the commutative properties, the associative properties, the distributive property, the identity properties, and the inverse properties.
  • Algebraic expressions are composed of constants and variables that are combined using addition, subtraction, multiplication, and division. They take on a numerical value when evaluated by replacing variables with constants.
  • Formulas are equations in which one quantity is represented in terms of other quantities. They may be simplified or evaluated as any mathematical expression.

Exercises

Verbal

  1. Is2an example of a rational terminating, rational repeating, or irrational number? Tell why it fits that category.
Show Solution

irrational number. The square root of two does not terminate, and it does not repeat a pattern. It cannot be written as a quotient of two integers, so it is irrational.

  1. What is the order of operations? What acronym is used to describe the order of operations, and what does it stand for?
  1. What do the Associative Properties allow us to do when following the order of operations? Explain your answer.
Show Solution

The Associative Properties state that the sum or product of multiple numbers can be grouped differently without affecting the result. This is because the same operation is performed (either addition or subtraction), so the terms can be re-ordered.

Numeric

For the following exercises, simplify the given expression.

  1. 10+2×(53)
  1. 6÷2(81÷32)
Show Solution

6

  1. 18+(68)3
  1. 2×[16÷(84)2]2
Show Solution

2

  1. 46+2×7
  1. 3(58)
Show Solution

9

  1. 4+610÷2
  1. 12÷(36÷9)+6
Show Solution

9

  1. (4+5)2÷3
  1. 312×2+19
Show Solution

-2

  1. 2+8×7÷4
  1. 5+(6+4)11
Show Solution

4

  1. 918÷32
  1. 14×3÷76
Show Solution

0

  1. 9(3+11)×2
  1. 6+2×21
Show Solution

9

  1. 64÷(8+4×2)
  1. 9+4(22)
Show Solution

25

  1. (12÷3×3)2
  1. 25÷527
Show Solution

6

  1. (157)×(37)
  1. 2×49(1)
Show Solution

17

  1. 4225×15
  1. 12(31)÷6
Show Solution

4

Algebraic

For the following exercises, solve for the variable.

  1. 8(x+3)=64
  1. 4y+8=2y
Show Solution

4

  1. (11a+3)18a=4
  1. 4z2z(1+4)=36
Show Solution

6

  1. 4y(72)2=200
  1. (2x)2+1=3
Show Solution

±1

  1. 8(2+4)15b=b
  1. 2(11c4)=36
Show Solution

2

  1. 4(31)x=4
  1. 14(8w42)=0
Show Solution

2

For the following exercises, simplify the expression.

  1. 4x+x(137)
  1. 2y(4)2y11
Show Solution

14y11

  1. a23(64)12a÷6
  1. 8b4b(3)+1
Show Solution

4b+1

  1. 5l÷3l×(96)
  1. 7z3+z×62
Show Solution

43z3

  1. 4×3+18x÷912
  1. 9(y+8)27
Show Solution

9y+45

  1. (96t4)2
  1. 6+12b3×6b
Show Solution

6b+6

  1. 18y2(1+7y)
  1. (49)2×27x
Show Solution

16x3

  1. 8(3m)+1(8)
  1. 9x+4x(2+3)4(2x+3x)
Show Solution

9x

  1. 524(3x)

Real-World Applications

For the following exercises, consider this scenario: Fred earns $40 mowing lawns. He spends $10 on mp3s, puts half of what is left in a savings account, and gets another $5 for washing his neighbor’s car.

  1. Write the expression that represents the number of dollars Fred keeps (and does not put in his savings account). Remember the order of operations.
Show Solution

12(4010)+5

  1. How much money does Fred keep?

For the following exercises, solve the given problem.

  1. According to the U.S. Mint, the diameter of a quarter is 0.955 inches. The circumference of the quarter would be the diameter multiplied byπ.Is the circumference of a quarter a whole number, a rational number, or an irrational number?
Show Solution

irrational number

  1. Jessica and her roommate, Adriana, have decided to share a change jar for joint expenses. Jessica put her loose change in the jar first, and then Adriana put her change in the jar. We know that it does not matter in which order the change was added to the jar. What property of addition describes this fact?

For the following exercises, consider this scenario: There is a mound ofgpounds of gravel in a quarry. Throughout the day, 400 pounds of gravel is added to the mound. Two orders of 600 pounds are sold and the gravel is removed from the mound. At the end of the day, the mound has 1,200 pounds of gravel.

  1. Write the equation that describes the situation.
Show Solution

g+4002(600)=1200

  1. Solve for g.

For the following exercise, solve the given problem.

  1. Ramon runs the marketing department at his company. His department gets a budget every year, and every year, he must spend the entire budget without going over. If he spends less than the budget, then his department gets a smaller budget the following year. At the beginning of this year, Ramon got $2.5 million for the annual marketing budget. He must spend the budget such that2,500,000x=0.What property of addition tells us what the value of x must be?
Show Solution

inverse property of addition

Technology

For the following exercises, use a graphing calculator to solve for x. Round the answers to the nearest hundredth.

  1. 0.5(12.3)248x=35
  1. (0.250.75)2x7.2=9.9
Show Solution

68.4

Extensions

  1. If a whole number is not a natural number, what must the number be?
  1. Determine whether the statement is true or false: The multiplicative inverse of a rational number is also rational.
Show Solution

true

  1. Determine whether the statement is true or false: The product of a rational and irrational number is always irrational.
  1. Determine whether the simplified expression is rational or irrational:184(5)(1).
Show Solution

irrational

  1. Determine whether the simplified expression is rational or irrational:16+4(5)+5.
  1. The division of two whole numbers will always result in what type of number?
Show Solution

rational

  1. What property of real numbers would simplify the following expression:4+7(x1)?

Glossary

algebraic expression
constants and variables combined using addition, subtraction, multiplication, and division
associative property of addition
the sum of three numbers may be grouped differently without affecting the result; in symbols,a+(b+c)=(a+b)+c
associative property of multiplication
the product of three numbers may be grouped differently without affecting the result; in symbols,a(bc)=(ab)c
base
in exponential notation, the expression that is being multiplied
commutative property of addition
two numbers may be added in either order without affecting the result; in symbols,a+b=b+a
commutative property of multiplication
two numbers may be multiplied in any order without affecting the result; in symbols,ab=ba
constant
a quantity that does not change value
distributive property
the product of a factor times a sum is the sum of the factor times each term in the sum; in symbols,a(b+c)=ab+ac
equation
a mathematical statement indicating that two expressions are equal
exponent
in exponential notation, the raised number or variable that indicates how many times the base is being multiplied
exponential notation
a shorthand method of writing products of the same factor
formula
an equation expressing a relationship between constant and variable quantities
identity property of addition
there is a unique number, called the additive identity, 0, which, when added to a number, results in the original number; in symbols,a+0=a
identity property of multiplication
there is a unique number, called the multiplicative identity, 1, which, when multiplied by a number, results in the original number; in symbols,a1=a
integers
the set consisting of the natural numbers, their opposites, and 0:{,3,2,1,0,1,2,3,}
inverse property of addition
for every real numbera, there is a unique number, called the additive inverse (or opposite), denoteda,which, when added to the original number, results in the additive identity, 0; in symbols,a+(a)=0
inverse property of multiplication
for every non-zero real numbera, there is a unique number, called the multiplicative inverse (or reciprocal), denoted1a, which, when multiplied by the original number, results in the multiplicative identity, 1; in symbols,a1a=1
irrational numbers
the set of all numbers that are not rational; they cannot be written as either a terminating or repeating decimal; they cannot be expressed as a fraction of two integers
natural numbers
the set of counting numbers:{1,2,3,}
order of operations
a set of rules governing how mathematical expressions are to be evaluated, assigning priorities to operations
rational numbers
the set of all numbers of the formmn,wheremandnare integers andn0.Any rational number may be written as a fraction or a terminating or repeating decimal.
real number line
a horizontal line used to represent the real numbers. An arbitrary fixed point is chosen to represent 0; positive numbers lie to the right of 0 and negative numbers to the left.
real numbers
the sets of rational numbers and irrational numbers taken together
variable
a quantity that may change value
whole numbers
the set consisting of 0 plus the natural numbers:{0,1,2,3,}

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