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Q.If y = sin⁻¹(2x / (1 + x²)) then find dy/dx.

Punjab PsebPSEB Punjab Class 12 Board 2019Subjective· 2mImportance★★★★★
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Substitute x=tan⁡θx=\tan\theta to simplify sin⁡−1 ⁣(2x1+x2)\sin^{-1}\!\left(\dfrac{2x}{1+x^2}\right) to 2tan⁡−1x2\tan^{-1}x, then differentiate.

y=sin⁡−1 ⁣(2x1+x2)y = \sin^{-1}\!\left(\dfrac{2x}{1+x^2}\right).

Let x=tan⁡θx = \tan\theta, so θ=tan⁡−1x\theta = \tan^{-1}x. Then:

2x1+x2=2tan⁡θ1+tan⁡2θ=sin⁡2θ\frac{2x}{1+x^2} = \frac{2\tan\theta}{1+\tan^2\theta} = \sin 2\theta

So for −1≤x≤1-1 \le x \le 1 (i.e. θ∈[−π/4,π/4]\theta\in[-\pi/4,\pi/4]): …

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