Calculus 8th Edition

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

Chapter 3 - Applications of Differentiation - 3.9 Antiderivatives - 3.9 Exercises - Page 283: 35

Answer

$$ f^{\prime \prime}(x)=-2+12 x-12 x^{2} ,\quad f(0)=4 ,\quad f^{\prime}(0)=12 $$ The required function is $$ f(x)=-x^{2}+2 x^{3}-x^{4}+12 x+4 $$

Work Step by Step

$$ f^{\prime \prime}(x)=-2+12 x-12 x^{2} ,\quad f(0)=4 ,\quad f^{\prime}(0)=12 $$ The general anti-derivative of $ f^{\prime \prime}(x)=-2+12 x-12 x^{2} $ is $$ f^{\prime}(x)=-2 x+6 x^{2}-4 x^{3}+C $$ To determine C we use the fact that $f^{\prime}(0)=12 $: $$ f^{\prime}(0)=-2 (0)+6(0)^{2}-4 (0)^{3}+C =12 $$ $ \Rightarrow $ $$ 0+C=12\quad \Rightarrow \quad C=12, $$ so $$ f^{\prime}(x)=-2 x+6 x^{2}-4 x^{3}+12 $$ Using the anti-differentiation rules once more, we find that: $$ f(x)=-x^{2}+2 x^{3}-x^{4}+12 x+D $$ To determine D we use the fact that $f(0)=4 $: $$ f(0)=-(0)^{2}+2 (0)^{3}-(0)^{4}+12 (0)+D =4 $$ $ \Rightarrow $ $$ 0+D=4\quad \Rightarrow \quad D=4, $$ so the required function is $$ f(x)=-x^{2}+2 x^{3}-x^{4}+12 x+4 $$
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