ARITHMETIC AND BASIC ALGEBRA

Transcription

1 C O M P E T E N C Y ARITHMETIC AND BASIC ALGEBRA. Add, subtract, multiply and divide rational numbers expressed in various forms Addition can be indicated by the expressions sum, greater than, and, more than, increased by, and added to. Subtraction can be expressed by difference, fewer than, minus, less than, decreased by, and subtracted from. Addition and subtraction can be demonstrated with symbols, as shown in the following example. ccczzzz Multiplication is shown by product, times, multiplied by, and twice. Multiplication can be shown using arrays. For instance, may be expressed as 3 rows of 4 each: u u u u u u u u u u u u Division is expressed by quotient, divided by, and ratio. As with multiplication, division can be demonstrated with an array. For example, can be shown by placing 2 objects in 2 rows: u u u u u u u u u u u u So it is obvious that the answer is 6. Examples: 7 added to a number n 7 a number decreased by 8 n times a number divided by 7 2n less than a number n 2 28 n 55 the ratio of a number to 55 4 times the sum of a number and 2 4(n 2) T e a c h e r c e r T i f i c a T i o n S T u d y G u i d e 3

2 Mathematical operations can be shown using manipulatives or drawings. Fractions can be clarified using pattern blocks, fraction bars, or paper folding. Generally, when applying these operations to rational numbers, the same rules apply. Any rational number can be expressed as a fraction with a finite numerator and finite denominator. Even whole numbers (such as 0,, 2, etc.) can be expressed as fractions ( 0, etc.).,, 2 For addition or subtraction of rational fractions, the numerators can be added or subtracted when the denominators are equal. For instance: If the denominators are different, find the least common denominator and convert the fractions appropriately. For instance: ( ) For multiplication of two fractions, the result is simply the product of the numerators over the product of the denominators Division involves multiplication by the reciprocal of the divisor. Thus, for example: When performing operations on decimals, one option is to convert the decimals to fractions (this may be helpful when multiplying long decimals that can be represented as simple fractions). A calculator can be used for performing operations on whole numbers or decimals, but be aware that the answer may not be accurate. The limitations of calculator technology mean that, for instance, the answer to may show up as , but the actual result is 0. 8 (an infinite number of eights after the decimal point)..2 Apply the order of operations The order of operations must be followed when evaluating algebraic expressions. The mnemonic pemdas (Please Excuse My Dear Aunt Sally) can help you to remember the order of the following steps.. Simplify inside grouping characters such as parentheses (P for Please), brackets, radicals, fraction bars, and so on. 2. Multiply out expressions with exponents (E for Excuse). 4 p r a x i S i i M i d d L e S c h o o L M a T h e M a T i c S , 5 6 9

3 3. Do multiplication (M for My) or division (D for Dear) from left to right. 4. Do addition (A for Aunt) or subtraction (S for Sally) from left to right. Here are some samples of simplifying expressions with exponents: simplified expressions WItH exponents ({2) 3 5 {8 {2 3 5 {8 ({2) {2 4 5 {6 note change of sign. ( 2 3 ) { Identify the properties of the basic operations on the standard number systems (e.g., closure, commutativity, associativity, distributivity) Real numbers exhibit the following addition and multiplication properties, where a, b, and c are real numbers. Note: Multiplication is implied when there is no symbol between two variables. Thus, a 3 b can be written ab. Multiplication can also be indicated by a raised dot? as in (a? b). Closure The Closure Property for Whole-Number Addition states that the sum of any two whole numbers is a whole number. Example: Since 2 and 5 are both whole numbers, 7 is also a whole number. The Closure Property for Whole-Number Multiplication states that the product of any two whole numbers is a whole number. T e a c h e r c e r T i f i c a T i o n S T u d y G u i d e 5

4 ARITHMETIC AND BASIC ALGEBRA Example: Since 3 and 4 are both whole numbers, 2 is also a whole number. The sum or product of two whole numbers is a whole number. For any set of numbers to be closed under an operation, the result of the operation on two numbers in the set must also be included within that set. Commutativity a b 5 b a Example: 5 {8 5 {8 5 5 {3 ab 5 ba Example: { {2 5 {2 The order of the addends or factors does not affect the sum or product. Associativity (a b) c 5 a (b c) Example: ({2 7) 5 5 {2 (7 5) { (ab)c 5 a(bc) Example: (3 3 {7) ({7 3 5) { {35 5 {05 The grouping of the addends or factors does not affect the sum or product. Distributivity a(b c) 5 ab ac Example: 6 3 ({4 9) 5 (6 3 {4) (6 3 9) { To multiply a sum by a number, multiply each addend by the number, and then add the products. Additive Identity (Property of Zero) a 0 5 a Example: The sum of any number and zero is that number. 6 p r a x i s i i m i d d l e s c h o o l m a t h e m a t i c s , 5 6 9

5 Multiplicative Identity (Property of One) a 3 5 a Example: { {34 The product of any number and is that number..4 Identify an inverse and the additive and multiplicative inverses of a number An INVERSE of a number can have one of two senses: an additive inverse, which involves negation of the number (or, equivalently, multiplication by {), or a multiplicative inverse, which involves the reciprocal of the number (or, equivalently, applying an exponent of { to the number). Thus, for any number a, the additive inverse is {a, and the multiplicative inverse is. Inverse numbers obey the a following properties. Additive Inverse (Property of Opposites) a {a 5 0 Example: 25 { INVERSE: the inverse of a number can have one of two senses: an additive inverse, which involves negation of the number, or a multiplicative inverse, which involves the reciprocal of the number The sum of any number and its opposite is zero. Multiplicative Inverse (Property of Reciprocals) a 3 a 5 Example: The product of any number and its reciprocal is. These inverse operations are used when solving equations..5 Use numbers in a way that is most appropriate in the context of a problem See Skill.3 for more on estimation and approximation T e a c h e r c e r T i f i c a T i o n S T u d y G u i d e 7

6 Example: The 7 a.m. train from the suburbs into the city has fi ve cars that each carry a maximum of 46 passengers. All of the cars are nearly full of passengers. Each passenger has about the same amount of cash. Approximately how much cash is on the train? A. $500 B. $0,000 C. $00,000 D. $50,000 The most logical answer is b, because the train is carrying about 230 people. Most of the passengers probably have $20 to $50 each..6 Order any fi nite set of real numbers and recognize equivalent forms of a number Property of Denseness Between any pair of rational numbers, there is at least one rational number. The set of natural numbers is not dense because between two consecutive natural numbers, there may not exist another natural number. Example: Between 7.6 and 7.7, there is the rational number 7.65 in the set of real numbers. Between 3 and 4, there exists no other natural number. If we compare numbers in various forms, we see that: The integer (fraction) (decimal) 5 400% (percent). 2 From this, you should be able to determine that fractions, decimals, and percents can be used interchangeably within problems. To change a percent into a decimal, move the decimal point two places to the left and drop off the percent sign. To change a decimal into a percent, move the decimal two places to the right and add on a percent sign. To change a fraction into a decimal, divide the numerator by the denominator. To change a decimal number into an equivalent fraction, write the decimal part of the number as the fraction's numerator. As the fraction's denominator, use the place value of the last column of the decimal. Reduce the resulting fraction as far as possible. 8 p r a x i S i i M i d d L e S c h o o L M a T h e M a T i c S , 5 6 9

7 Example: J.C. Nickels has Hunch jeans for sale at 25% off the usual price of $ Shears and Roadster have the same jeans for sale at 30% off their regular price of $40. Find the cheaper price. 5.25, so.25(36) 5 $9.00 off; $ $27 sale price 4 30% 5.30, so.30(40) 5 $2 off; $ $28 sale price The price at J.C Nickels is $ lower. To convert a fraction to a decimal, as we did in the example above, simply divide the numerator (top) by the denominator (bottom). Use long division if necessary. If a decimal has a fixed number of digits, the decimal is said to be a TERMINATING DECIMAL. To write such a decimal as a fraction, first determine what place value the digit farthest to the right has (for example: tenths, hundredths, thousandths, ten-thousandths, hundred-thousandths, etc.). Then drop the decimal point and place the string of digits over the number given by the place value. If a decimal continues forever by repeating a string of digits, the decimal is said to be a REPEATING DECIMAL. To write a repeating decimal as a fraction, follow these steps:. Let x 5 the repeating decimal (Ex. x ) 2. Multiply x by the multiple of 0 that will move the decimal just to the right of the repeating block of digits (Ex. 000x ) TERMINATING DECIMAL: a decimal that has a fi xed number of digits REPEATING DECIMAL: a decimal that continues forever by repeating a string of digits 3. Subtract the first equation from the second (Ex. 000x 2 x ) 4. Simplify and solve this equation. The repeating block of digits will subtract out (Ex. 999x 5 76 so x ) 5. The solution will be the fraction for the repeating decimal CoMMoN equivalents % % % % % Table continued on next page T e a c h e r c e r T i f i c a T i o n S T u d y G u i d e 9

8 % % % % % % % % Decimal values have been rounded off to the hundredths place..7 Classify a number as rational, irrational, real, or complex Real Numbers REAL NUMBERS: numbers that can be shown by an infi nite decimal representation such as Irrational Numbers Natural Numbers Whole Numbers Integers Rational Numbers For a listing of mathematical symbols, go to: wiki/math_symbols REAL NUMBERS are denoted by R and are numbers that can be shown by an infinite decimal representation such as The real numbers include rational numbers such as 42 and 23/29, and irrational numbers such as Ï 2 and p, which can be represented as points along an infinite number line. Real numbers are also known as the unique complete Archimedean ordered field. Real numbers are differentiated from imaginary numbers. 0 p r a x i S i i M i d d L e S c h o o L M a T h e M a T i c S , 5 6 9

9 ARITHMETIC AND BASIC ALGEBRA Properties of Real Numbers Real numbers have the two primary properties of being an ordered field and having the least upper-bound property. The First Property says that real numbers comprise an ordered field (with addition and multiplication, as well as division by nonzero numbers) that can be ordered on a number line in a way that works with addition and multiplication. Example: O is an ordered field if the order satisfies the following properties: If a # b, then a c # b c. If 0 # a and 0 # b, then 0 # ab. It then follows that for every a, b, c, d in O: Either a # 0 # a or a # 0 # a. We can add inequalities: Example: If a # b and c # d, then a c # b d. We are allowed to multiply inequalities with positive elements : If a # b and 0 # c, then ac # bc. The Second Property of real numbers says that if a nonempty set of real numbers has an upper bound (e.g., #, or less than or equal to), then it has a least upper bound. These two properties together define the real numbers completely and allow their other properties to be inferred: Every polynomial of odd degree with real coefficients has a real root. If you add the square root of to the real numbers, you have a complex number, and the result is algebraically closed. Real numbers are classified as follows: Natural numbers, denoted by N: the counting numbers,2,3,... Whole numbers: the counting numbers along with zero 0,,2... Integers, denoted by Z: the counting numbers, their opposites, and zero..., {,0,,... Rationals, denoted by Q: all of the fractions that can be formed from the whole numbers. Zero cannot be the denominator. In decimal form, these numbers will either be terminating or repeating decimals. Simplify square roots to determine if the number can be written as a fraction. Irrationals: real numbers that cannot be written as a fraction. The decimal forms of these numbers are neither terminating nor repeating. Examples: p, e, Ï 2, and so on Real numbers, denoted by R: the set of numbers obtained by combining the rationals and the irrationals. T e a c h e r C e r t i f i c a t i o n S t u d y G u i d e

10 ARITHMETIC AND BASIC ALGEBRA Complex Numbers Complex numbers, i.e. numbers that involve i or Ï {, are not real numbers. Complex numbers generally include all numbers that have a real and an imaginary part. The imaginary part of a complex number is some real number (which may be zero) multiplied by i (or Ï { ). Thus, the general form of a complex number is a bi, where a and b are real numbers. Since it is possible that b 5 0, the set of complex numbers includes the set of real numbers. Properties of complex numbers We just reviewed real numbers; real numbers can be ordered, but complex numbers cannot be ordered When i appears in a fraction, the fraction is usually simplified so that i is not in the denominator The complex plane and complex numbers as ordered pairs Every complex number a bi can be shown as a pair of two real numbers. For the real part a and the imaginary part bi, b is also real. Example: 3i has a real part 0 and an imaginary part 3, and 4 has a real part 4 and an imaginary part 0. As another way of writing complex numbers, we can write them as ordered pairs: Complex Number Ordered Pair 3 2i (3, 2) Ï 3, Ï 3i ( Ï 3, Ï 3 ) 7i (0, 7) 6 2i ( ) 7 6 7, 2 7 When i 2 appears in a problem, it can be replaced by {, since i 2 5 {. How do we turn into {? We can work with what is called a complex plane and visually see how it can be done. Instead of an x-axis and a y-axis, we have an axis that represents the real dimension and an axis that represents the imaginary dimension. If we rotate x 80 in a counterclockwise direction, we can change into {, which is the same as multiplying by i 2. 2 p r a x i s i i m i d d l e s c h o o l m a t h e m a t i c s , 5 6 9

11 imaginary numbers 2 90 multiply by i 2 (i * i) 5 { i 80 { {2 { {i 2 real numbers { {2 We could also rotate clockwise 80 to turn { into. This is a multiplication by i 2. If we multiply {i by {i, we get {. Therefore, there are two square roots of {: i and {i..8 Estimate values of expressions involving decimals, exponents, and radicals Exponents The EXPONENT FORM is a shortcut method to write repeated multiplication. The BASE is the factor being multiplied. The EXPONENT tells how many times that number is multiplied by itself. Example: 3 4 is , where 3 is the base and 4 is the exponent. x 2 is read as x squared. y 3 is read as y cubed. EXPONENT FORM: a shortcut method to write repeated multiplication BASE: the factor being multiplied EXPONENT: tells how many times that number is multiplied by itself T e a c h e r c e r T i f i c a T i o n S T u d y G u i d e 3

12 a 5 a for all values of a; thus, b 0 5 for all values of b; thus, When 0 is raised to any power, the exponent tells the number of zeros in the product. Example: ,000,000 rules of exponents a x a y 5 a x y Example: (3 4 )(3 5 ) a x b x 5 (ab) x Example: (4 2 )(5 2 ) (a x ) y 5 a xy Example: (2 3 ) a x 4 a y 5 a x 2 y Example: a {x 5 Example: 2 a {2 5 x 2 2 SCIENTIFIC NOTATION: a method for writing very large and very small numbers Scientifi c Notation SCIENTIFIC NOTATION is a more convenient method for writing very large and very small numbers. It employs two factors: a number between {0 and 0 and a power of 0. This notation is a shorthand way to express large numbers, such as the weight of 00 freight cars in kilograms, or small numbers, such as the weight of an atom in grams. CoMMoN Measures using scientific NotatIoN 0 n 5 (0) n Ten multiplied by itself n times 0 6 5,000,000 (mega) (kilo) (hecto) (deca) any nonzero number raised to the zero power is 0-5 0{ (deci) (centi) Table continued on next page 4 p r a x i S i i M i d d L e S c h o o L M a T h e M a T i c S , 5 6 9

13 ARITHMETIC AND BASIC ALGEBRA 0{ (milli) 0{6 5,000,000 (micro) To write a number in scientific notation, convert the number to a form of b 3 0 n, where {0, b, 0 and n is an integer. Example: can be written in various forms: { () {2 (2) (3) (4) (5) Only (4) is written in the proper scientific notation format, because (b) is a number between {0 and 0. To change a number into scientific notation, move the decimal point so that only one number from to 9 is in front of the decimal point. Remove any trailing zeros. Multiply this number times 0 to a power. The power is the number of positions that the decimal point is moved. The power is negative if the original number is a decimal number between and {. Otherwise, the power is positive. Example: Change into scientific notation: 4,380,000,000 Move decimal behind the Remove trailing zeros ? Count the positions that the decimal point has moved This is the answer. { Move the decimal behind the 4. {4.07 Count the positions that the decimal point has moved. { Note the negative exponent. If a number is already in scientific notation, it can be changed back into the regular decimal form. If the exponent on the number 0 is negative, move the decimal point to the left. If the exponent on the number 0 is positive, move the decimal point to the right that number of places. Example: Write 46,368,000 in scientific notation.. Introduce a decimal point: 46,368, ,368, Move the decimal place to the left until only one nonzero digit is in front of it in this case, between the 4 and the 6. T e a c h e r C e r t i f i c a t i o n S t u d y G u i d e 5

14 ARITHMETIC AND BASIC ALGEBRA 3. Count the number of digits that the decimal point has moved in this case, 7. This is the nth power of ten, and it is positive because the decimal point moved left. 4. Therefore, 46,368, Example: Write in scientific notation.. The decimal point is already in place. 2. Move the decimal point to the right until there is only one nonzero digit in front of it in this case, between the 3 and the Count the number of digits the decimal point moved in this case, 3. This is the nth power of ten, and it is negative because the decimal point moved right. 4. Therefore, {3. Example: Evaluate { {6 Since we have a mixture of large and small numbers, convert each number to scientific notation: { { {5 Thus, we have { { { { {3 3 0 { { { { ,000,000 Example: Change back into decimal form: {2 Move the decimal point 2 places left, since the exponent is negative This is the answer Move the decimal point 4 places right, since the exponent is positive. 60,000 This is the answer. 6 p r a x i s i i m i d d l e s c h o o l m a t h e m a t i c s , 5 6 9