Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 3 - Applications of Differentiation - Review - Exercises - Page 287: 57

Answer

$$ f^{\prime \prime}(x)=1-6x +48 x^{2} ,\quad f(0)=1 ,\quad f^{\prime}(0)=2 $$ The required function is $$ f(x)=\frac{1}{2}x^{2}-x^{3} +4x^{4}+2x+1. $$

Work Step by Step

$$ f^{\prime \prime}(x)=1-6x +48 x^{2} ,\quad f(0)=1 ,\quad f^{\prime}(0)=2 $$ The general anti-derivative of $ f^{\prime \prime}(x)=1-6x +48 x^{2} $ is $$ f^{\prime}(x)=x-3x^{2} +16 x^{3}+C $$ To determine C we use the fact that $f^{\prime}(0)=2 $: $$ f^{\prime}(0)=(0)-3(0)^{2} +16 (0)^{3}+C =2 $$ $ \Rightarrow $ $$ 0+C=2\quad \Rightarrow \quad C=2, $$ so $$ f^{\prime}(x)=x-3x^{2} +16 x^{3}+2 $$ Using the anti-differentiation rules once more, we find that: $$ f(x)=\frac{1}{2}x^{2}-x^{3} +4x^{4}+2x+D $$ To determine D we use the fact that $f(0)=1 $: $$ f(0)=\frac{1}{2}(0)^{2}-(0)^{3} +4(0)^{4}+2(0)+D=1 $$ $ \Rightarrow $ $$ 0+D=1\quad \Rightarrow \quad D=1, $$ so the required function is $$ f(x)=\frac{1}{2}x^{2}-x^{3} +4x^{4}+2x+1. $$
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