Calculus Concepts: An Informal Approach to the Mathematics of Change 5th Edition

Published by Brooks Cole
ISBN 10: 1-43904-957-2
ISBN 13: 978-1-43904-957-0

Chapter 3 - Determining Change: Derivatives - 3.7 Activities - Page 244: 15

Answer

$$\lim _{x \rightarrow 2} \frac{2 x^{2}-5 x+2}{5 x^{2}-7 x-6} =\frac{3}{13}$$

Work Step by Step

Given $$\lim _{x \rightarrow 2} \frac{2 x^{2}-5 x+2}{5 x^{2}-7 x-6}$$ using the method of replacement \begin{align*} \lim _{x \rightarrow 2} \frac{2 x^{2}-5 x+2}{5 x^{2}-7 x-6}&=\lim _{x \rightarrow 2} \frac{2 (2)^{2}-5(2)+2}{5 (2)^{2}-7 (2)-6}\\ &=\frac{0}{0} \end{align*} This is an indeterminate form, then applying L'Hôpital's Rule, we get \begin{align*} \lim _{x \rightarrow 2} \frac{2 x^{2}-5 x+2}{5 x^{2}-7 x-6}&= \lim _{x \rightarrow 2} \frac{4 x-5}{10 x-7 }\\ &= \lim _{x \rightarrow 2} \frac{4(2)-5}{10(2)-7 }\\ &=\lim _{x \rightarrow 2}\frac{3}{13}\\ &=\frac{3}{13} \end{align*}
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