MCQ
જો  $\sin \left(\frac{y}{x}\right)=\log _0|x|+\frac{\alpha}{2}$ એ વિકલ સમીકરણ  $x \cos \left(\frac{y}{x}\right) \frac{d y}{d x}=y \cos \left(\frac{y}{x}\right)+x$ નો ઉકેલ હોય તથા $y(1)=\frac{\pi}{3}$, હોય, તો  $\alpha^2$ =..................
  • A
    $3$
  • B
    $12$
  • C
    $4$
  • D
    $9$

Answer

Differential equation :-

$ x \cos \frac{y}{x} \frac{d y}{d x}=y \cos \frac{y}{x}+x $

$ \cos \frac{y}{x}\left[x \frac{d y}{d x}-y\right]=x$

Divide both sides by $\mathrm{x}^2$

$\cos \frac{y}{x}\left(\frac{x \frac{d y}{d x}-y}{x^2}\right)=\frac{1}{x}$

Let $\frac{y}{x}=t$

$\cos t\left(\frac{d t}{d x}\right)=\frac{1}{x}$

$\cos \mathrm{t} \mathrm{dt}=\frac{1}{\mathrm{x}} \mathrm{dx}$

Integrating both sides

$ \sin \mathrm{t}=\ln |\mathrm{x}|+\mathrm{c} $

$ \sin \frac{\mathrm{y}}{\mathrm{x}}=\ln |\mathrm{x}|+\mathrm{c}$

Using $y(1)=\frac{\pi}{3}$, we get $c=\frac{\sqrt{3}}{2}$

So, $\alpha=\sqrt{3} \Rightarrow \alpha^2=3$

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