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- 1. CHAPTER 0 Review *This chapter consists of review material. It may be used as the first part of the course or later as ajust-in-time review when the content is required. Specific references to this chapter occur throughoutthe book to assist in the review process.
- 2. 0.1 Real NumbersPREPARING FOR THIS SECTION Before getting started, review the following:OBJECTIVES 1 Classify numbers 2 Evaluate numerical expressions 3 Work with properties of real numbersSetsWhen we want to treat a collection of similar but distinct objects as a whole, we use the idea of a set. Forexample, the set of digits consists of the collection of numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. If we use thesymbol D to denote the set of digits, then we can writeIn this notation, the braces { } are used to enclose the objects, or elements, in the set. This method ofdenoting a set is called the roster method . A second way to denote a set is to use set-builder notation,where the set D of digits is written asread as “D is the set of all x such that x is a digit.” EXAMPLE 1 Using Set-Builder Notation and the Roster Method (a) E = { x | x is an even digit} = {0, 2, 4, 6, 8} (b) O = { x | x is an odd digit} = {1, 3, 5, 7, 9}In listing the elements of a set, we do not list an element more than once because the elements of a set aredistinct. Also, the order in which the elements are listed is not relevant. For example, {2, 3} and {3, 2}both represent the same set.If every element of a set A is also an element of a set B, then we say that A is a subset of B. If two sets Aand B have the same elements, then we say that A equals B. For example, {1, 2, 3} is a subset of {1, 2, 3,4, 5}, and {1, 2, 3} equals {2, 3, 1}.Finally, if a set has no elements, it is called the empty set , or the null set , and is denoted by the symbolØ.
- 3. Classification of NumbersIt is helpful to classify the various kinds of numbers that we deal with as sets. The counting numbers, ornatural numbers, are the numbers in the set {1, 2, 3, 4, …}. (The three dots, called an ellipsis , indicatethat the pattern continues indefinitely.) As their name implies, these numbers are often used to countthings. For example, there are 26 letters in our alphabet; there are 100 cents in a dollar. The wholenumbers are the numbers in the set {0, 1, 2, 3, …}, that is, the counting numbers together with 0. The integers are the numbers in the set {…, −3, −2, −1,0,1,2,3, …}.These numbers are useful in many situations. For example, if your checking account has $10 in it and youwrite a check for $15, you can represent the current balance as −$5.Notice that the set of counting numbers is a subset of the set of whole numbers. Each time we expand anumber system, such as from the whole numbers to the integers, we do so in order to be able to handlenew, and usually more complicated, problems. The integers allow us to solve problems requiring bothpositive and negative counting numbers, such as profit/loss, height above/below sea level, temperatureabove/below 0°F, and so on.But integers alone are not sufficient for all problems. For example, they do not answer the question“What part of a dollar is 38 cents?" To answer such a question, we enlarge our number system to includerational numbers. For example, answers the question “What part of a dollar is 38 cents?” A rational number is a number that can be expressed as a quotient of two integers. The integer a is called the numerator , and the integer b, which cannot be 0, is called the denominator . The rational numbers are the numbers in the set { where a and b, b ≠ 0, are integers}.Examples of rational numbers are , , , , and . Since for any integer a, it follows that theset of integers is a subset of the set of rational numbers.Rational numbers may be represented as decimals. For example, the rational numbers , , , andmay be represented as decimals by merely carrying out the indicated division:Notice that the decimal representations of and terminate, or end. The decimal representations ofand do not terminate, but they do exhibit a pattern of repetition. For , the 6 repeats indefinitely;for , the block 06 repeats indefinitely. It can be shown that every rational number may be representedby a decimal that either terminates or is nonterminating with a repeating block of digits, and vice versa.
- 4. On the other hand, there are decimals that do not fit into either of these categories. Such decimalsrepresent irrational numbers. Every irrational number may be represented by a decimal that neitherrepeats nor terminates. In other words, irrational numbers cannot be written in the form , where a and b,b ≠ 0, are integers.Irrational numbers occur naturally. For example, consider the isosceles right triangle whose legs are eachof length 1. See Figure 1. The length of the hypotenuse is , an irrational number. FIGURE 1Also, the number that equals the ratio of the circumference C to the diameter d of any circle, denoted bythe symbol π (the Greek letter pi), is an irrational number. See Figure 2. FIGURE 2 Together, the rational numbers and irrational numbers form the set of real numbers.Figure 3 shows the relationship of various types of numbers. FIGURE 3
- 5. 1 EXAMPLE 2 Classifying the Numbers in a SetList the numbers in the setthat are (a) Natural numbers (b) Integers (c) Rational numbers (d) Irrational numbers (e) Real numbers
- 6. SOLUTION (a) 10 is the only natural number. (b) −3 and 10 are integers. (c) and 10 are rational numbers. (d) and π are irrational numbers. (e) All the numbers listed are real numbers. NOW WORK PROBLEM 3.ApproximationsEvery decimal may be represented by a real number (either rational or irrational), and every real numbermay be represented by a decimal.The irrational numbers and π have decimal representations that begin as follows:In practice, decimals are generally represented by approximations. For example, using the symbol ≈ (readas “approximately equal to”), we can writeIn approximating decimals, we either round off or truncate to a given number of decimal places. Thenumber of places establishes the location of the final digit in the decimal approximation. Truncation: Drop all the digits that follow the specified final digit in the decimal. Rounding: Identify the specified final digit in the decimal. If the next digit is 5 or more, add 1 to the final digit; if the next digit is 4 or less, leave the final digit as it is. Now truncate following the final digit.
- 7. EXAMPLE 3 Approximating a Decimal to Two PlacesApproximate 20.98752 to two decimal places by (a) Truncating (b) RoundingSOLUTIONFor 20.98752, the final digit is 8, since it is two decimal places from the decimal point. (a) To truncate, we remove all digits following the final digit 8. The truncation of 20.98752 to two decimal places is 20.98. (b) To round, we examine the digit following the final digit 8, which is 7. Since 7 is 5 or more, we add 1 to the final digit 8 and truncate. The rounded form of 20.98752 to two decimal places is 20.99. EXAMPLE 4 Approximating a Decimal to Two and Four Places Rounded to Rounded to Truncated to Truncated to Two Decimal Four Decimal Two Decimal Four Decimal Number Places Places Places Places (a) 3.14159 3.14 3.1416 3.14 3.1415 (b) 0.056128 0.06 0.0561 0.05 0.0561 (c) 893.46125 893.46 893.4613 893.46 893.4612
- 8. NOW WORK PROBLEM 7.CalculatorsCalculators are finite machines. As a result, they are incapable of displaying decimals that contain a largenumber of digits. For example, some calculators are capable of displaying only eight digits. When anumber requires more than eight digits, the calculator either truncates or rounds. To see how yourcalculator handles decimals, divide 2 by 3. How many digits do you see? Is the last digit a 6 or a 7? If it isa 6, your calculator truncates; if it is a 7, your calculator rounds.There are different kinds of calculators. An arithmetic calculator can only add, subtract, multiply, anddivide numbers; therefore, this type is not adequate for this course. Scientific calculators have all thecapabilities of arithmetic calculators and also contain function keys labelled ln, log, sin, cos, tan, x y , inv,and so on. Graphing calculators have all the capabilities of scientific calculators and contain a screen onwhich graphs can be displayed.For those who have access to a graphing calculator, we have included comments, examples, and exercisesmarked with a , indicating that a graphing calculator is required. We have also included an Appendixthat explains some of the capabilities of a graphing calculator. The comments, examples, andexercises may be omitted without loss of continuity, if so desired.OperationsIn algebra, we use letters such as x, y, a, b, and c to represent numbers. The symbols used in algebra forthe operations of addition, subtraction, multiplication, and division are +, −, ·, and /. The words used todescribe the results of these operations are sum, difference, product, and quotient. Table 1 summarizesthese ideas. TABLE 1 Operation Symbol Words Addition a+b Sum: a plus b Subtraction a−b Difference: a minus b Multiplication a· b, (a)· b, a·(b), (a)·(b), ab, (a)b, a(b), (a)(b) Product: a times b Division a/b or Quotient:a divided by bWe generally avoid using the multiplication sign × and the division sign ÷ so familiar in arithmetic. Noticealso that when two expressions are placed next to each other without an operation symbol, as in ab, or inparentheses, as in (a)(b), it is understood that the expressions, called factors , are to be multiplied.We also prefer not to use mixed numbers.When mixed numbers are used, addition is understood; forexample, means . The use of a mixed number may be confusing because the absence of an
- 9. operation symbol between two terms is generally taken to mean multiplication. The expression istherefore written instead as 2.75 or as .The symbol =, called an equal sign and read as “equals” or “is,” is used to express the idea that thenumber or expression on the left of the equal sign is equivalent to the number or expression on the right. EXAMPLE 5 Writing Statements Using Symbols (a) The sum of 2 and 7 equals 9. In symbols, this statement is written as 2 + 7 = 9. (b) The product of 3 and 5 is 15. In symbols, this statement is written as 3 · 5 = 15. NOW WORK PROBLEM 19.Order of Operations2 Evalute numerical expressionsConsider the expression 2 + 3 · 6. It is not clear whether we should add 2 and 3 to get 5, and then multiplyby 6 to get 30; or first multiply 3 and 6 to get 18, and then add 2 to get 20. To avoid this ambiguity, wehave the following agreement. We agree that whenever the two operations of addition and multiplication separate three numbers, the multiplication operation will be performed first, followed by the addition operation.For example, we find 2 + 3 · 6 as follows: EXAMPLE 6 Finding the Value of an ExpressionEvaluate each expression. (a) 3 + 4 · 5 (b) 8 · 2 + 1
- 10. (c) 2 + 2 · 2SOLUTION (a) (b) (c) 2 + 2 · 2 = 2 + 4 = 6 NOW WORK PROBLEM 31.To first add 3 and 4 and then multiply the result by 5, we use parentheses and write (3 + 4) · 5. Wheneverparentheses appear in an expression, it means “perform the operations within the parentheses first!” EXAMPLE 7 Finding the Value of an Expression (a) (5 + 3) · 4 = 8 · 4 = 32 (b) (4 + 5) · (8 − 2) = 9 · 6 = 54When we divide two expressions, as init is understood that the division bar acts like parentheses; that is,The following list gives the rules for the order of operations.
- 11. Rules for the Order of Operations 1. Begin with the innermost parentheses and work outward. Remember that in dividing two expressions the numerator and denominator are treated as if they were enclosed in parentheses. 2. Perform multiplications and divisions, working from left to right. 3. Perform additions and subtractions, working from left to right. EXAMPLE 8 Finding the Value of an ExpressionEvaluate each expression. (a) 8 · 2 + 3 (b) 5 · (3 + 4) + 2 (c) (d) 2 + [4 + 2 · (10 + 6)]SOLUTION (a) (b)
- 12. (c) (d) NOW WORK PROBLEMS 37 AND 45.Properties of Real NumbersWork with properties of real numbersWe have used the equal sign to mean that one expression is equivalent to another. Four importantproperties of equality are listed next. In this list, a, b, and c represent numbers. 1. The reflexive property states that a number always equals itself; that is, a = a. 2. The symmetric property states that if a = b then b = a. 3. The transitive property states that if a = b and b = c then a = c. 4. The principle of substitution states that if a = b then we may substitute b for a in any expression containing a.Now, let’s consider some other properties of real numbers.We begin with an example. EXAMPLE 9 Commutative Properties (a)
- 13. (b)This example illustrates the commutative property of real numbers, which states that the order in whichaddition or multiplication takes place will not affect the final result. Commutative Properties (1a) (1b)Here, and in the properties listed next and on pages 10–13, a, b, and c represent real numbers. EXAMPLE 10 Associative Properties (a) (b)The way we add or multiply three real numbers will not affect the final result. So, expressions such as2 + 3 + 4 and 3 · 4 · 5 present no ambiguity, even though addition and multiplication are performed on onepair of numbers at a time. This property is called the associative property . Associative Properties (2a) (2b)
- 14. The next property is perhaps the most important. Distributive Property (3a)The distributive property may be used in two different ways. EXAMPLE 11 Distributive Property NOW WORK PROBLEM 63.The real numbers 0 and 1 have unique properties. EXAMPLE 12 Identity Properties (a) 4 + 0 = 0 + 4 = 4 (b) 3 · 1 = 1 · 3 = 3The properties of 0 and 1 illustrated in Example 12 are called the identity properties . Identity Properties (4a) (4b)We call 0 the additive identity and 1 the multiplicative identity.For each real number a, there is a real number − a, called the additive inverse of a, having the followingproperty:
- 15. Additive Inverse Property (5a) EXAMPLE 13 Finding an Additive Inverse (a) The additive inverse of 6 is −6, because 6 + (−6) = 0. (b) The additive inverse of −8 is −(−8) = 8, because −8 + 8 = 0.The additive inverse of a, that is, − a, is often called the negative of a or the opposite of a. The use ofsuch terms can be dangerous, because they suggest that the additive inverse is a negative number, which itmay not be. For example, the additive inverse of −3, namely −(−3), equals 3, a positive number.For each nonzero real number a, there is a real number , called the multiplicative inverse of a, havingthe following property: Multiplicative Inverse Property (5b)The multiplicative inverse of a nonzero real number a is also referred to as the reciprocal of a. EXAMPLE 14 Finding a Reciprocal (a) The reciprocal of 6 is , because . (b) The reciprocal of −3 is −3, because . (c) The reciprocal of is , because .
- 16. With these properties for adding and multiplying real numbers, we can now define the operations ofsubtraction and division as follows: The difference a − b, also read “ a less b” or “ a minus b,” is defined as (6)To subtract b from a, add the opposite of b to a. If b is a nonzero real number, the quotient , also read as “ a divided by b” or “the ratio of a to b,” is defined as (7) EXAMPLE 15 Working with Differences and Quotients (a) 8 − 5 = 8 + (−5) = 3 (b) 4 − 9 = 4 + (−9) =−5 (c)For any number a, the product of a times 0 is always 0. Multiplication by Zero (8)For a nonzero number a, we have the following division properties.
- 17. Division Properties (9)NOTE: Division by 0 is not defined. One reason is to avoid the following difficulty: means to find xsuch that 0 · x = 2. But 0 · x equals 0 for all x, so there is no number x such that . Rules of Signs (10) EXAMPLE 16 Applying the Rules of Signs (a) 2(−3) = −(2 · 3) = −6 (b) (−3)(−5) = 3 · 5 = 15 (c) (d) (e) Cancellation Properties
- 18. (11) EXAMPLE 17 Using the Cancellation Properties (a) If 2x = 6, then (b)NOTE: We follow the common practice of using slash marks to indicate cancellations. Zero-Product Property (12) EXAMPLE 18 Using the Zero-Product PropertyIf 2x = 0, then either 2 = 0 or x = 0. Since 2 ≠ 0, it follows that x = 0. Arithmetic of Quotients (13) (14)
- 19. (15) EXAMPLE 19 Adding, Subtracting, Multiplying, and Dividing Quotients (a) (b) (c) NOTE: Slanting the cancellation marks in different directions for different factors, as shown here, is a good practice to follow, since it will help in checking for errors. (d)NOTE: In writing quotients, we shall follow the usual convention and write the quotient in lowest terms;that is, we write it so that any common factors of the numerator and the denominator have been removedusing the cancellation properties, Equation 11. For example,
- 20. NOW WORK PROBLEMS 47, 51, AND 61.Sometimes it is easier to add two fractions using least common multiples (LCM). The LCM of twonumbers is the smallest number that each has as a common multiple. EXAMPLE 20 Finding the Least Common Multiple of Two NumbersFind the least common multiple of 15 and 12.To find the LCM of 15 and 12, we look at multiples of 15 and 12.SOLUTION 15, 30, 45, 60, 75, 90, 105, 120, … 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, …The common multiples are in blue. The least common multiple is 60. EXAMPLE 21 Using the Least Common Multiple to Add Two FractionsFind:SOLUTIONWe use the LCM of the denominators of the fractions and rewrite each fraction using the LCM as acommon denominator. The LCM of the denominators (12 and 15) is 60. Rewrite each fraction using 60 asthe denominator. NOW WORK PROBLEM 55.
- 21. EXERCISE 0.1In Problems 1–6, list the numbers in each set that are (a) natural numbers, (b) integers, (c)rational numbers, (d) irrational numbers, (e) real numbers.1.2.3.4.5.6.In Problems 7–18, approximate each number (a) rounded and (b) truncated to three decimalplaces.7. 18.95268. 25.861349. 28.6531910. 99.05249
- 22. 11. 0.0629112. 0.0538813. 9.998514. 1.000615.16.17.18.In Problems 19–28, write each statement using symbols.19. The sum of 3 and 2 equals 5.20. The product of 5 and 2 equals 10.21. The sum of x and 2 is the product of 3 and 4.22. The sum of 3 and y is the sum of 2 and 2.23. 3 times y is 1 plus 2.
- 23. 24. 2 times x is 4 times 6.25. x minus 2 equals 6.26. 2 minus y equals 6.27. x divided by 2 is 6.28. 2 divided by x is 6.In Problems 29–62, evaluate each expression.29. 9−4+230. 6−4+331. −6 + 4 · 332. 8−4·233. 4+5−834. 8−3−435.36.
- 24. 37. 6 − [3 · 5 + 2 · (3 − 2)]38. 2 · [8 − 3(4 + 2)] − 339. 2 · (3 − 5) + 8 · 2 − 140. 1 − (4 · 3 − 2 + 2)41. 10 − [6 − 2 · 2 + (8 − 3)] · 242. 2 − 5 · 4 − [6 · (3 − 4)]43.44.45.46.47.48.49.50.
- 25. 51.52.53.54.55.56.57.58.59.60.61.62.
- 26. In Problems 63–74, use the Distributive Property to remove the parentheses.63. 6(x + 4)64. 4(2x − 1)65. x(x − 4)66. 4x(x + 3)67. (x + 2)(x + 4)68. (x + 5)(x + 1)69. (x − 2)(x + 1)70. (x − 4)(x + 1)71. (x − 8)(x − 2)72. (x − 4)(x − 2)73. (x + 2)(x − 2)74. (x − 3)(x + 3)75. Explain to a friend how the Distributive Property is used to justify the fact that 2x + 3x = 5x.76. Explain to a friend why 2 + 3 · 4 = 14, whereas (2 + 3) · 4 = 20.
- 27. 77. Explain why 2(3 · 4) is not equal to (2 · 3) · (2 · 4).78. Explain why is not equal to .79. Is subtraction commutative? Support your conclusion with an example.80. Is subtraction associative? Support your conclusion with an example.81. Is division commutative? Support your conclusion with an example.82. Is division associative? Support your conclusion with an example.83. If 2 = x, why does x = 2?84. If x = 5, why does x2 + x = 30?85. Are there any real numbers that are both rational and irrational? Are there any real numbers that are neither? Explain your reasoning.86. Explain why the sum of a rational number and an irrational number must he irrational.87. What rational number does the repeating decimal 0.999

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