$\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
- $\frac{1}{2}$
- $\frac{1}{3}$
- $\frac{1}{4}$
- $\frac{1}{6}$
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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