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Name Date LESSON 9-5 Class Reteach Functions and Their Inverses Not all relations are functions and not all relations have inverse functions. To decide whether the inverse of a relation is a function, use the horizontal-line test. If any horizontal line passes through more than one point on the graph of a relation, the inverse of the relation is not a function. Y Y X X Can you draw a horizontal line that passes through more than one point on the graph? Can you draw a horizontal line that passes through more than one point on the graph? No. So the inverse of the relation is a function. Yes. So the inverse of the relation is NOT a function. Use the horizontal-line test to determine whether the inverse of each relation is a function. 1. 2. Y Y X Not a function 3. X Function 4. Y Y X Function Copyright © by Holt, Rinehart and Winston. All rights reserved. a207c09-5_rt.indd 38 X Not a function 38 Holt Algebra 2 1/4/06 7:05:48 PM Process Black Name LESSON 9-5 Date Class Reteach Functions and Their Inverses (continued) The inverse of a function, f x , is denoted f 1 x . To find the inverse of a function f x , write y f x . Then switch x and y and solve the equation for y. 2 Find the inverse of f x x 1. Step 1 Write y f x . 2 yx 1 Step 2 Switch x and y. 2 xy 1 Step 3 Solve for y. Isolate the variable, y. 2 xy 1 Take the square root of both sides. x 1 y2 x 1 2 y The domain is {x | x 1}. x 1 y Remember, x 1 can be either positive or negative. Because y could have 2 different x-values, x 1 and x 1 , this inverse is not a function. Check by graphing the original function on a graphing calculator and use the horizontal-line test. The domain of the inverse is the range of f x : { x | x 1 }. The range of the inverse is the domain of f x : all real numbers. Find the inverse of each function and state its domain and range. 3 5. f x x y x 3 y 2x 1 x y3 x 2y 1 x f 1 6. f x 2x 1 3 y x x 1 2y 1 x1 f x _____ 2 domain: all real numbers; range: all real numbers x 3 2 domain: all real numbers x such that x 3; range: nonnegative real numbers Copyright © by Holt, Rinehart and Winston. 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