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

  • question_answer
    If \[\cos x=\frac{1}{\sqrt{1+{{t}^{2}}}}\]and \[\sin y=\frac{t}{\sqrt{1+{{t}^{2}}}}\], then \[\frac{dy}{dx}=\] [MP PET 1994]

    A)            ?1

    B)            \[\frac{1-t}{1+{{t}^{2}}}\]

    C)            \[\frac{1}{1+{{t}^{2}}}\]

    D)            1

    Correct Answer: D

    Solution :

               Obviously \[x={{\cos }^{-1}}\frac{1}{\sqrt{1+{{t}^{2}}}}\]and \[y={{\sin }^{-1}}\frac{t}{\sqrt{1+{{t}^{2}}}}\]                    Þ \[\frac{dx}{dt}=-\frac{1}{\sqrt{\frac{{{t}^{2}}}{1+{{t}^{2}}}}}.\frac{(-1)}{2{{(1+{{t}^{2}})}^{3/2}}}2t=\frac{1}{1+{{t}^{2}}}\]                    and  \[\frac{dy}{dt}=\sqrt{1+{{t}^{2}}}.\frac{1}{{{(\sqrt{1+{{t}^{2}}})}^{3/2}}}=\frac{1}{1+{{t}^{2}}}\]            Hence \[\frac{dy}{dx}=\frac{dy/dt}{dx/dt}=1\].


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