Calculus 8th Edition

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

Chapter 2 - Derivatives - 2.6 Implicit Differentiation - 2.6 Exercises - Page 166: 21

Answer

$$\frac{-16}{13}$$

Work Step by Step

Given $$f(x) +x^2[f(x)]^3=10$$ Differentiate the both sides \begin{align*} f'(x)+3x^2[f(x)]^2f'(x)+2x[f(x)]^3&=0\\ f'(x) (1+3x^2[f(x)]^2 )&=-2x[f(x)]^3\\ f'(x) &= \frac{-2x[f(x)]^3}{1+3x^2[f(x)]^2}\\ \end{align*} Since $f(1)= 2$, then \begin{align*} f'(1) &= \frac{-2(1)[f(1)]^3}{1+3(1)^2[f(1)]^2}\\ &= \frac{-2(8)}{1+3(4)}\\ &=\frac{-16}{13} \end{align*}
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