If \(x=\sin \theta\) and \(y=\cos p \theta\), then \(\left(1-x^2\right) y_2=\)

If \(x=\sin \theta\) and \(y=\cos p \theta\), then \(\left(1-x^2\right) y_2=\)
  1. \(x y_1-p^2 y\)
  2. \(p^2 y-x y_1\)
  3. \(x y_1\)
  4. \(p^2 y\)

Solution

Given, \(x=\sin \theta\) and \(y=\cos p \theta\) \(\therefore \quad \frac{d y}{d \theta}=-p \sin p \theta\) and \(\frac{d x}{d \theta}=\cos \theta\) \(\Rightarrow \quad \frac{d y}{d x}=-\frac{p \sin p \theta}{\cos \theta}=-p \frac{\sqrt{1-y^2}}{\sqrt{1-x^2}}\) \(\Rightarrow \sqrt{1-x^2} \frac{d y}{d x}=-p \sqrt{1-y^2}\) \(\Rightarrow \quad\left(\mathrm{l}-x^2\right)\left(\frac{d y}{d x}\right)^2=p^2\left(\mathrm{l}-y^2\right)\) (On squaring both sides) \(\Rightarrow-2 x\left(\frac{d y}{d x}\right)^2+\left(\mathrm{l}-x^2\right) 2 \frac{d y}{d x}\left(\frac{d^2 y}{d x^2}\right)=-p^2 2 y \frac{d y}{d x}\) (On differentiating both sides) \(\Rightarrow \quad-x \frac{d y}{d x}+\left(1-x^2\right) \frac{d^2 y}{d x^2}=-p^2 y\) \(\Rightarrow \quad\left(\mathrm{l}-x^2\right) y_2=x y_1-p^2 y\) Hence, option (a) is correct.

Asked in: AP EAMCET 2019 (23 Apr Shift 1)

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