JEE Main & Advanced Mathematics Differentiation Question Bank Differentiation by Substitution

  • question_answer
    If \[y=a{{e}^{mx}}+b{{e}^{-mx}}\], then \[\frac{{{d}^{2}}y}{d{{x}^{2}}}-{{m}^{2}}y=\]     [MP PET 1987]

    A)            \[{{m}^{2}}(a{{e}^{mx}}-b{{e}^{-mx}})\]

    B)            1

    C)            0

    D)            None of these

    Correct Answer: C

    Solution :

               \[y=a{{e}^{mx}}+b{{e}^{-mx}};\] \[\therefore \frac{dy}{dx}=am{{e}^{mx}}-mb{{e}^{-mx}}\]            Again \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=a{{m}^{2}}{{e}^{mx}}+{{m}^{2}}b{{e}^{-mx}}\]            Þ \[\frac{{{d}^{2}}y}{d{{x}^{2}}}={{m}^{2}}(a{{e}^{mx}}+b{{e}^{-mx}})\Rightarrow \frac{{{d}^{2}}y}{d{{x}^{2}}}={{m}^{2}}y\]            or \[\frac{{{d}^{2}}y}{d{{x}^{2}}}-{{m}^{2}}y=0\].


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