Holt McDougal Algebra Inverses of Relations and Functions 4-2 Inverses of Relations and Functions Holt Algebra 2 Warm Up Warm Up Lesson Presentation Lesson Presentation Lesson Quiz Lesson Quiz Holt McDougal Algebra 2

4-2 Inverses of Relations and Functions Warm Up Solve for y. 1. x = 3y –7 4. x = y 2 3. x = 4 – y 2. x = y x y = y = 8x – 5 y = 4 – x y = ± x

Holt McDougal Algebra Inverses of Relations and Functions Graph and recognize inverses of relations and functions. Find inverses of functions. Objectives

Holt McDougal Algebra Inverses of Relations and Functions inverse relation inverse function Vocabulary

Holt McDougal Algebra Inverses of Relations and Functions You have seen the word inverse used in various ways. The additive inverse of 3 is –3. The multiplicative inverse of 5 is The multiplicative inverse matrix of

Holt McDougal Algebra Inverses of Relations and Functions You can also find and apply inverses to relations and functions. To graph the inverse relation, you can reflect each point across the line y = x. This is equivalent to switching the x- and y- values in each ordered pair of the relation. A relation is a set of ordered pairs. A function is a relation in which each x-value has, at most, one y-value paired with it. Remember!

Holt McDougal Algebra Inverses of Relations and Functions Graph the relation and connect the points. Then graph the inverse. Identify the domain and range of each relation. Example 1: Graphing Inverse Relations x 0158 y 2569 Graph each ordered pair and connect them. x 2569 y 0158 ● ● ● ● Switch the x- and y-values in each ordered pair.

Holt McDougal Algebra Inverses of Relations and Functions Example 1 Continued Reflect each point across y = x, and connect them. Make sure the points match those in the table. Domain:{x|0 ≤ x ≤ 8} Range :{y|2 ≤ x ≤ 9} Domain:{x|2 ≤ x ≤ 9} Range :{y|0 ≤ x ≤ 8}

Holt McDougal Algebra Inverses of Relations and Functions Graph the relation and connect the points. Then graph the inverse. Identify the domain and range of each relation. x y Check It Out! Example 1 Graph each ordered pair and connect them. x y Switch the x- and y-values in each ordered pair.

Holt McDougal Algebra Inverses of Relations and Functions Reflect each point across y = x, and connect them. Make sure the points match those in the table. Domain:{1 ≤ x ≤ 6} Range :{0 ≤ y ≤ 5} Domain:{0 ≤ y ≤5} Range :{1 ≤ x ≤ 6} Check It Out! Example 1 Continued

Holt McDougal Algebra Inverses of Relations and Functions When the relation is also a function, you can write the inverse of the function f(x) as f –1 (x). This notation does not indicate a reciprocal. Functions that undo each other are inverse functions. To find the inverse function, use the inverse operation. In the example above, 6 is added to x in f(x), so 6 is subtracted to find f –1 (x).

Holt McDougal Algebra Inverses of Relations and Functions Use inverse operations to write the inverse of f(x) = x – if possible. Example 2: Writing Inverses of by Using Inverse Functions 1 2 is subtracted from the variable, x. 1 2 Add to x to write the inverse. 1 2 f(x) = x – f –1 (x) = x +

Holt McDougal Algebra Inverses of Relations and Functions Example 2 Continued Substitute 1 for x. Check Use the input x = 1 in f(x). f(x) = x – 1 2 f(1) = 1 – Substitute for x. Substitute the result into f –1 (x) 1 2 f –1 (x) = x + = 1 = f –1 ( ) = The inverse function does undo the original function.

Holt McDougal Algebra Inverses of Relations and Functions Use inverse operations to write the inverse of f(x) =. x 3 Check It Out! Example 2a f –1 (x) = 3x f(x) = The variable x, is divided by 3. Multiply by 3 to write the inverse. x 3

Holt McDougal Algebra Inverses of Relations and Functions Substitute 1 for x. Check Use the input x = 1 in f(x). 1 3 Substitute for x. Substitute the result into f –1 (x) = 1 = 1 3 f –1 ( ) = 3( ) The inverse function does undo the original function. Check It Out! Example 2a Continued f(x) = x 3 f(1) = 1 3 f –1 (x) = 3x

Holt McDougal Algebra Inverses of Relations and Functions Use inverse operations to write the inverse of f(x) = x +. Check It Out! Example 2b is added to the variable, x. 2 3 Subtract from x to write the inverse. 2 3 f(x) = x f –1 (x) = x – 2 3

Holt McDougal Algebra Inverses of Relations and Functions Check It Out! Example 2b Continued Substitute 1 for x. Check Use the input x = 1 in f(x). f(1) = Substitute for x. Substitute the result into f –1 (x) 2 3 f –1 (x) = x – = 1 = f –1 ( ) = – The inverse function does undo the original function. f(x) = x + 2 3

Holt McDougal Algebra Inverses of Relations and Functions Undo operations in the opposite order of the order of operations. The reverse order of operations: Addition or Subtraction Multiplication or Division Exponents Parentheses Helpful Hint

Holt McDougal Algebra Inverses of Relations and Functions Use inverse operations to write the inverse of f(x) = 3(x – 7). The variable x is subtracted by 7, then is multiplied by 3. First, undo the multiplication by dividing by 3. Then, undo the subtraction by adding 7. Example 3: Writing Inverses of Multi-Step Functions f(x) = 3(x – 7) 1 3 f –1 (x) = x + 7 Check Use a sample input. f(9) = 3(9 – 7) = 3(2) = f –1 (6) = (6) + 7= 2 + 7= 9

Holt McDougal Algebra Inverses of Relations and Functions Use inverse operations to write the inverse of f(x) = 5x – 7. The variable x is multiplied by 5, then 7 is subtracted. First, undo the subtraction by adding by 7. Then, undo the multiplication by dividing by 5. f(x) = 5x – 7. Check Use a sample input. Check It Out! Example 3 f –1 (x) = x f –1 (3) = = = 2 f(2) = 5(2) – 7 =

Holt McDougal Algebra Inverses of Relations and Functions You can also find the inverse function by writing the original function with x and y switched and then solving for y.

Holt McDougal Algebra Inverses of Relations and Functions Example 4: Writing and Graphing Inverse Functions Switch x and y. Solve for y. Set y = f(x) and graph f. Graph f(x) = – x – 5. Then write the inverse and graph y = – x – x = – y – 5x + 5 = – y 1 2 –2x – 10 = y Write in y = format. y = –2(x + 5)

Holt McDougal Algebra Inverses of Relations and Functions Example 4 Continued Set y = f(x). f –1 (x) = –2(x + 5) Simplify. Then graph f –1. f –1 (x) = –2x – 10 f f –1

Holt McDougal Algebra Inverses of Relations and Functions Switch x and y. Solve for y. Set y = f(x) and graph f. Graph f(x) = x + 2. Then write the inverse and graph. 2 3 x – 2 = y 2 3 3x – 6 = 2y Write in y = format. Check It Out! Example x = y y = x + 2 x – 3 = y 3 2

Holt McDougal Algebra Inverses of Relations and Functions Set y = f(x). Then graph f –1. f f –1 Check It Out! Example 4 f –1 (x) = x – 3 3 2

Holt McDougal Algebra Inverses of Relations and Functions Anytime you need to undo an operation or work backward from a result to the original input, you can apply inverse functions. In a real-world situation, don’t switch the variables, because they are named for specific quantities. Remember!

Holt McDougal Algebra Inverses of Relations and Functions Lesson Quiz: Part I 1. A relation consists of the following points and the segments drawn between them. Find the domain and range of the inverse relation: D:{x|1  x  8}R:{y|0  y  9} x03469 y12578

Holt McDougal Algebra Inverses of Relations and Functions Lesson Quiz: Part II 2. Graph f(x) = 3x – 4. Then write and graph the inverse. f –1 (x) = x f f –1

Holt McDougal Algebra Inverses of Relations and Functions Lesson Quiz: Part III 3. A thermometer gives a reading of 25° C. Use the formula C = (F – 32). Write the inverse function and use it to find the equivalent temperature in °F. 5 9 F = C + 32; 77° F 9 5

Holt McDougal Algebra Inverses of Relations and Functions HW: Text Pg 245 Tuesday (1/13) #4-16 Wednesday (1/14) # 20 – 40 even, 41 – 46 all