J & K CET Engineering J and K - CET Engineering Solved Paper-2004

  • question_answer
    \[y=a{{e}^{mx}}+b{{e}^{-mx}}\] satisfies which of the following differential equations

    A)  \[\frac{dy}{dx}-my=0\]

    B)  \[\frac{dy}{dx}+my=0\]

    C)  \[\frac{{{d}^{2}}y}{d{{x}^{2}}}-{{m}^{2}}y=0\]

    D)  None of these

    Correct Answer: C

    Solution :

    Given equation is \[y=a{{e}^{mx}}+b{{e}^{-mx}}\] On differentiating w.r.t. x, we get               \[\frac{dy}{dx}=m\,a{{e}^{mx}}-m\,b{{e}^{-mx}}\] Again differentiating, we get \[\frac{{{d}^{2}}y}{d{{x}^{2}}}={{m}^{2}}\,a{{e}^{mx}}+{{m}^{2}}b{{e}^{-mx}}\] \[={{m}^{2}}(a{{e}^{mx}}+b{{e}^{-mx}})={{m}^{2}}y\] \[\Rightarrow \] \[\frac{{{d}^{2}}y}{d{{x}^{2}}}-{{m}^{2}}y=0\]


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