Intermediate Algebra (12th Edition)

Published by Pearson
ISBN 10: 0321969359
ISBN 13: 978-0-32196-935-4

Chapter 9 - Section 9.1 - Inverse Functions - 9.1 Exercises - Page 589: 20

Answer

one-to-one function inverse: $f^{-1}(x)=x^2-2,\text{ }x\ge0$

Work Step by Step

Some of the ordered pairs of the given function, $ f(x)=\sqrt{x+2},\text{ }x\ge-2 $, are $ \left\{(-2,0)(-1,1),(2,2),(7,3),(14,4),...\right\} $. Note that every $y$-coordinate from this function is unique. Hence, the given function is a one-to-one function. To find the inverse, let $y=f(x)$. Then, interchange the $x$ and $y$ variables and solve for $y$. That is, \begin{align*}\require{cancel} y&=\sqrt{x+2},\text{ }x\ge-2 \\&\Rightarrow x=\sqrt{y+2},\text{ }y\ge-2 &(\text{interchange $x$ and $y$}) \\ &(\text{* Note that $y\ge-2$ implies $x\ge0$.}) \\& (x)^2=\left(\sqrt{y+2}\right)^2,\text{ }x\ge0 &(\text{solve for $y$}) \\& x^2=y+2 \\& x^2-2=y \\& y=x^2-2 .\end{align*} Hence, the inverse is $ f^{-1}(x)=x^2-2,\text{ }x\ge0 $.
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