If $\tan ^{-1}(2 x)+\tan ^{-1}(3 x)=\frac{\pi}{4}$, where $x>0$, then $x=$
If $\tan ^{-1}(2 x)+\tan ^{-1}(3 x)=\frac{\pi}{4}$, where $x>0$, then $x=$
- 1
- $\frac{1}{6}$
- $\frac{1}{3}$
- $\frac{1}{2}$
Solution
$\begin{aligned}
& \tan ^{-1}(2 x)+\tan ^{-1}(3 x)=\frac{\pi}{4} \\
& \therefore \tan ^{-1}\left[\frac{2 x+3 x}{1-(2 x)(3 x)}\right]=\frac{\pi}{4} \Rightarrow \tan \frac{\pi}{4}=\frac{5 x}{1-6 x^2}=1 \\
& \therefore 6 x^2+5 x-1=0 \Rightarrow(6 x-1)(x+1)=0 \Rightarrow x=-1, \frac{1}{6}
\end{aligned}$
Since $x>0$, we get $x=\frac{1}{6}$
Asked in: MHT CET 2021 (24 Sep Shift 1)
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