Considering only the Principal values of inverse functions, the set $A=\left\{x \geq 0 \left\lvert\, \tan…

Considering only the Principal values of inverse functions, the set $A=\left\{x \geq 0 \left\lvert\, \tan ^{-1}(2 x)+\tan ^{-1}(3 x)=\frac{\pi}{4}\right.\right\}$
  1. contains two elements.
  2. contains more than two elements.
  3. is an empty set.
  4. is a singleton set.

Solution

$\begin{aligned} & \tan ^{-1}(2 x)+\tan ^{-1}(3 x)=\frac{\pi}{4} \\ \therefore \quad & \tan ^{-1}\left(\frac{2 x+3 x}{1-(2 x)(3 x)}\right)=\frac{\pi}{4}\end{aligned}$ $\begin{array}{ll} \therefore & \frac{5 x}{1-6 x^2}=\tan \left(\frac{\pi}{4}\right) \\ \therefore & 5 x=1-6 x^2 \\ \therefore & 6 x^2+5 x-1=0 \\ \therefore & 6 x^2+6 x-x-1=0 \\ \therefore & (6 x-1)(x+1)=0 \\ \therefore & x=\frac{1}{6} \ldots[\because x \geq 0] \end{array}$ $\therefore \quad$ set A is a singleton set.

Asked in: MHT CET 2024 (04 May Shift 1)

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