JEE Main & Advanced Mathematics Differentiation Question Bank Derivative at a point Standard Differentiation

  • question_answer
    If \[y=\frac{{{e}^{2x}}\cos x}{x\sin x},\]then \[\frac{dy}{dx}=\]                                [AI CBSE 1982]

    A)            \[\frac{{{e}^{2x}}[(2x-1)\cot x-x\,\text{cose}{{\text{c}}^{2}}x]}{{{x}^{2}}}\]

    B)            \[\frac{{{e}^{2x}}[(2x+1)\cot x-x\,\text{cose}{{\text{c}}^{2}}x]}{{{x}^{2}}}\]

    C)            \[\frac{{{e}^{2x}}[(2x-1)\cot x+x\,\text{cose}{{\text{c}}^{2}}x]}{{{x}^{2}}}\]

    D)            None of these

    Correct Answer: A

    Solution :

               \[y=\frac{{{e}^{2x}}\cos x}{x\sin x}\]Þ \[\log y=2x+\log \cos x-\log x-\log \sin x\]                    \[\frac{1}{y}\frac{dy}{dx}=2+\left( \frac{-\sin x}{\cos x} \right)-\frac{1}{x}-\frac{\cos x}{\sin x}\]                    Þ  \[\frac{dy}{dx}={{e}^{2x}}\left[ \frac{2}{x}\cot x-\frac{1}{x}-\frac{1}{{{x}^{2}}}\cot x-\frac{{{\cot }^{2}}x}{x} \right]\]                               \[=\frac{{{e}^{2x}}}{{{x}^{2}}}[(2x-1)\cot x-x\,\text{cose}{{\text{c}}^{2}}x]\].


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