$\lim _{x \rightarrow 0^{+}} \frac{x \sin ^{-1}\left(\frac{2 x}{1+x^2}\right)}{\cos…

$\lim _{x \rightarrow 0^{+}} \frac{x \sin ^{-1}\left(\frac{2 x}{1+x^2}\right)}{\cos ^{-1}\left(\frac{1-x^2}{1+x^2}\right) \tan ^{-1}\left(\frac{3 x-x^3}{1-3 x^2}\right)}$ is equal to
  1. $\frac{1}{2}$
  2. $\frac{1}{3}$
  3. $\frac{1}{4}$
  4. $\frac{1}{6}$

Solution

$ \lim _{x \rightarrow 0^{+}} \frac{x \sin ^{-1}\left(\frac{2 x}{1+x^2}\right)}{\cos ^{-1}\left(\frac{1-x^2}{1+x^2}\right) \cdot \tan ^{-1}\left(\frac{3 x-x^3}{1-3 x^2}\right)} $ $\because$ We know that $x \rightarrow 0^{+}$ $ \begin{aligned} & 2 \tan ^{-1} x=\sin ^{-1} \frac{2 x}{1+x^2}=\cos ^{-1}\left(\frac{1-x^2}{1+x^2}\right) \\ & 3 \tan ^{-1} x=\tan ^{-1}\left(\frac{3 x-x^3}{1-3 x^2}\right) \end{aligned} $ $\therefore$ Limit becomes $ \lim _{x \rightarrow 0^{+}} \frac{x \cdot\left(2 \tan ^{-1} x\right)}{\left(2 \tan ^{-1} x\right)\left(3 \tan ^{-1} x\right)} $ $ \Rightarrow \lim _{x \rightarrow 0^{+}} \frac{x}{3 \tan ^{-1} x} $ Using L Hospital rule $ \lim _{x \rightarrow 0^{+}}=\frac{1}{3 \times \frac{1}{1+x^2}}=\frac{1}{3 \times\left(\frac{1}{1+0}\right)}=\frac{1}{3} $

Asked in: AP EAMCET 2021 (24 Aug Shift 1)

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