Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 7: Transcendental Functions - Section 7.6 - Inverse Trigonometric Functions - Exercises 7.6 - Page 421: 98

Answer

$1$

Work Step by Step

Multiply the limit with $\displaystyle \frac{x^{2}}{x^{2}}$ and rewrite: $L=\displaystyle \lim_{x\rightarrow 0^{+}}\frac{\sin^{-1}x^{2}}{x^{2}}\cdot\lim_{x\rightarrow 0^{+}}\frac{x^{2}}{(\sin^{-1}x)^{2}}=L_{1}\cdot L_{2}$ $L_{1}=\displaystyle \lim_{x\rightarrow 0^{+}}\frac{\sin^{-1}x^{2}}{x^{2}}\qquad $... substitute $\left[\begin{array}{l} t=x^{2}\\ t\rightarrow 0^{+} \end{array}\right]$ $L_{1}=\displaystyle \lim_{t\rightarrow 0^{+}}\frac{\sin^{-1}t}{t}\qquad $... $\displaystyle \frac{0}{0}$, apply L'Hopital's rule See table 7-4,$ \displaystyle \quad \frac{d(\sin^{-1}u)}{dx}=\frac{1}{\sqrt{1-u^{2}}}\frac{du}{dx}, |u| \lt 1$ $L_{1}=\displaystyle \lim_{t\rightarrow 0^{+}}\frac{\frac{1}{\sqrt{1-t^{2}}}}{1}=\lim_{t\rightarrow 0^{+}}\frac{1}{\sqrt{1-t^{2}}}=1$ $L_{2}=\displaystyle \lim_{x\rightarrow 0^{+}}\frac{x^{2}}{(\sin^{-1}x)^{2}}=[\lim_{x\rightarrow 0^{+}}\frac{x}{\sin^{-1}x}]^{2}$ The limit has the form $\displaystyle \frac{0}{0}$; apply L'Hopital's rule $L_{2}= [\displaystyle \lim_{x\rightarrow 0^{+}} \displaystyle \frac{1}{\frac{1}{\sqrt{1-x^{2}}}}]^{2}=[\lim_{x\rightarrow 0^{+}}\sqrt{1-x^{2}}=1]^{2}$ $L_{1}\cdot L_{2}=1\cdot 1=1$
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