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

  • question_answer
    If \[y=f\left( \frac{5x+1}{10{{x}^{2}}-3} \right)\]and \[f'(x)=\cos x\], then \[\frac{dy}{dx}=\] [MP PET 1987]

    A)            \[\cos \,\left( \frac{5x+1}{10{{x}^{2}}-3} \right)\,\frac{dy}{dx}\,\left( \frac{5x+1}{10{{x}^{2}}-3} \right)\]

    B)            \[\frac{5x+1}{10{{x}^{2}}-3}\,\,\cos \,\left( \frac{5x+1}{10{{x}^{2}}-3} \right)\]

    C)            \[\cos \,\left( \frac{5x+1}{10{{x}^{2}}-3} \right)\]              

    D)            None of these

    Correct Answer: A

    Solution :

               Suppose that \[t=\frac{5x+1}{10{{x}^{2}}-3},\] so \[y=f(t)\]                    \[\therefore \,\,\frac{dy}{dx}={f}'(t).\frac{dt}{dx}\]                        [Since \[f'(x)=\cos x\]]                             \[\frac{dy}{dx}=\cos \left( \frac{5x+1}{10{{x}^{2}}-3} \right)\,\frac{d}{dx}\,\left( \frac{5x+1}{10{{x}^{2}}-3} \right).\]


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