Question
Find $\frac{d y}{d x}$, if $x^{\frac{2}{3}}+y^{\frac{2}{3}}=a^{\frac{2}{3}}$.

Answer

Let x = a cos3 $\theta$,  y = aSin3$\theta$
Then $\frac{d x}{d \theta}$ = -3a cos2 $\theta$ sin $\theta$
  and $\frac{d y}{d \theta}$ = 3a sin2 $\theta$ cos $\theta$
Therefore,  $\frac{d y}{d x}=\frac{\frac{d y}{d x}}{\frac{d x}{d \theta}}=\frac{3 a \sin ^{2} \theta \cos \theta}{-3 a \cos ^{2} \theta \sin \theta}=-\tan \theta=-\sqrt[3]{\frac{y}{x}}$

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