Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 2 - Limits - 2.5 Evaluating Limits Algebraically - Exercises - Page 72: 19

Answer

$$\lim _{h \rightarrow 0} \frac{\frac{1}{(h+2)^{2}}-\frac{1}{4}}{h} =-\frac{1}{4} $$

Work Step by Step

Given $$\lim _{h \rightarrow 0} \frac{\frac{1}{(h+2)^{2}}-\frac{1}{4}}{h}$$ let $$ f(h) = \frac{\frac{1}{(h+2)^{2}}-\frac{1}{4}}{h}$$ Since, we have $$ f(0)= \frac{\frac{1}{4}-\frac{1}{4}}{0}=\frac{0}{0}$$ So, transform algebraically and cancel \begin{aligned}L&= \lim _{h \rightarrow 0} \frac{\frac{1}{(h+2)^{2}}-\frac{1}{4}}{h} \\ & = \lim _{h \rightarrow 0} \frac{\frac{4-(h+2)^{2}}{4(h+2)^{2}}}{h}\\ &= \lim _{h \rightarrow 0} \frac{\frac{4-\left(h^{2}+4 h+4\right)}{4(h+2)^{2}}}{h}\\ &= \lim _{h \rightarrow 0} \frac{4-h^{2}-4 h-4}{4(h+2)^{2} h}\\ &= \lim _{h \rightarrow 0} \frac{-h^{2}-4 h}{4 h(h+2)^{2}}\\ &= \lim _{h \rightarrow 0} \frac{-h(h+4)}{4 h(h+2)^{2}}\\ &=\lim _{h \rightarrow 0} \frac{-(h+4)}{4(h+2)^{2}} \\ &=\frac{-(0+4)}{4(0+2)^{2}} \\ &=\frac{-(4)}{4 (2)^{2}} \\ &=\frac{-(4)}{16} \\ &=-\frac{1}{4} \\ \end{aligned}
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