JEE Main & Advanced Mathematics Differentiation Question Bank Differentiation of implicit function Parametric

  • question_answer
    If \[x=a{{\cos }^{4}}\theta ,y=a{{\sin }^{4}}\theta ,\] then \[\frac{dy}{dx}\], at \[\theta =\frac{3\pi }{4}\], is [Kerala (Engg.) 2002]

    A)            ?1

    B)            1

    C)            \[-{{a}^{2}}\]

    D)            \[{{a}^{2}}\]

    Correct Answer: A

    Solution :

               \[y=a{{\sin }^{4}}\theta \] Þ \[\frac{dy}{d\theta }=4a{{\sin }^{3}}\theta \cos \theta \]            and \[x=a{{\cos }^{4}}\theta \]  Þ \[\frac{dx}{d\theta }=-4a{{\cos }^{3}}\theta \sin \theta \]            \ \[\frac{dy}{dx}=\frac{dy/d\theta }{dx/d\theta }=\frac{-{{\sin }^{2}}\theta }{{{\cos }^{2}}\theta }=-{{\tan }^{2}}\theta \]            \   \[{{\left( \frac{dy}{dx} \right)}_{\theta =\frac{3\pi }{4}}}=-{{\tan }^{2}}\left( \frac{3\pi }{4} \right)=-1\].


You need to login to perform this action.
You will be redirected in 3 sec spinner