Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 3 - The Derivative - Chapter Review - Review Exercises - Page 190: 55

Answer

$$ \begin{aligned} y &=4 x^{2}+3 x-2=f(x) \\ y^{\prime} &=\lim _{h \rightarrow 0} \frac{f(x+h)-f(x)}{h} \\ &=\lim _{h \rightarrow 0} \frac{\left[4(x+h)^{2}+3(x+h)-2\right]-\left[4 x^{2}+3 x-2\right]}{h} \\ &=\lim _{h \rightarrow 0} \frac{4\left(x^{2}+2 x h+h^{2}\right)+3 x+3 h-2-4 x^{2}-3 x+2}{h} \\ &=\lim _{h \rightarrow 0} \frac{\left.4 x^{2}+8 x h+h^{2}\right)+3 x+3 h-2-4 x^{2}-3 x+2}{h} \\ &=\lim _{h \rightarrow 0} \frac{8 x h+4 h^{2}+3 x+3 h-2-4 x^{2}-3 x+2}{h} \\ &=\lim _{h \rightarrow 0} \frac{8 x h+4 h+3)}{h} \\ &=\lim _{h \rightarrow 0}(8 x+4 h+3) \\ &=8 x+3 \end{aligned} $$ Thus the derivative of the given function is $$ y^{\prime}=8 x+3 $$

Work Step by Step

$$ \begin{aligned} y &=4 x^{2}+3 x-2=f(x) \\ y^{\prime} &=\lim _{h \rightarrow 0} \frac{f(x+h)-f(x)}{h} \\ &=\lim _{h \rightarrow 0} \frac{\left[4(x+h)^{2}+3(x+h)-2\right]-\left[4 x^{2}+3 x-2\right]}{h} \\ &=\lim _{h \rightarrow 0} \frac{4\left(x^{2}+2 x h+h^{2}\right)+3 x+3 h-2-4 x^{2}-3 x+2}{h} \\ &=\lim _{h \rightarrow 0} \frac{\left.4 x^{2}+8 x h+h^{2}\right)+3 x+3 h-2-4 x^{2}-3 x+2}{h} \\ &=\lim _{h \rightarrow 0} \frac{8 x h+4 h^{2}+3 x+3 h-2-4 x^{2}-3 x+2}{h} \\ &=\lim _{h \rightarrow 0} \frac{8 x h+4 h+3)}{h} \\ &=\lim _{h \rightarrow 0}(8 x+4 h+3) \\ &=8 x+3 \end{aligned} $$ Thus the derivative of the given function is $$ y^{\prime}=8 x+3 $$
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