Finite Math and Applied Calculus (6th Edition)

Published by Brooks Cole
ISBN 10: 1133607705
ISBN 13: 978-1-13360-770-0

Chapter 11 - Section 11.1 - Derivatives of Powers, Sums, and Constant Multiples - Exercises - Page 795: 82

Answer

L'Hospital's rule applies. limit = $ -12$

Work Step by Step

Theorem 11.3 L'Hospital's Rule: If $f$ and $g$ are differentiable functions such that substituting $x=a$ in the expression $\displaystyle \frac{f(x)}{g(x)}$ gives the indeterminate form $\displaystyle \frac{0}{0}$ or $\displaystyle \frac{\infty}{\infty}$, then $\displaystyle \lim_{x\rightarrow a}\frac{f(x)}{g(x)}=\lim_{x\rightarrow a} \displaystyle \frac{f^{\prime}(x)}{\mathrm{g}^{\prime}(x)}$. That is, we can replace $f(x)$ and $g(x)$ with their derivatives and try again to take the limit. -------------------- When x approaches $-2$, (evaluating for x=$-2$) the numerator approaches $(-2)^{3}+8=-8+8=0$ the denominator approaches $4-6+2=0$ $\displaystyle \frac{f(x)}{g(x)}$ is of indeterminate form $\displaystyle \frac{0}{0}$, L'Hospital's rule applies. $\displaystyle \lim_{x\rightarrow-2}\frac{x^{3}+8}{x^{2}+3x+2}=\lim_{x\rightarrow-2} \displaystyle \frac{[x^{3}+8]^{\prime}}{[x^{2}+3x+2]^{\prime}}$ $=\displaystyle \lim_{x\rightarrow-2} \displaystyle \frac{3x^{2}+0}{2x+3+0}=$ $=\displaystyle \frac{3(2^{2})}{-4+3}=\frac{12}{-1}=-12$
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