Discrete Mathematics and Its Applications, Seventh Edition

Published by McGraw-Hill Education
ISBN 10: 0073383090
ISBN 13: 978-0-07338-309-5

Chapter 2 - Section 2.3 - Functions - Exercises - Page 154: 36

Answer

$\text{f o g}(x)=x^2+4x+5$ $\text{g o f}(x)=x^2+3$

Work Step by Step

Given $g: \cal{R}\rightarrow \cal{R}$ and $f: \cal{R}\rightarrow \cal{R}$ $$f(x)=x^2+1$$$$g(x)=x+2$$ Since f and g are both functions from $\cal{R}$ to $\cal{R}$, $\text{f o g}$ and $\text{g o f}$ are also functions from $\cal{R}$ to $\cal{R}$. Use the definition of composition: $$\text{f o g}(x)=f(g(x))=fxX+2)=(x+2)^2+1=x^2+4x+5$$$$\text{g o f}(x)=g(f(x))=g(x^2+1)=(x^2+1)+1=x^2+3$$
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