JCECE Engineering JCECE Engineering Solved Paper-2009

  • question_answer
    Find the differential equation of curves \[y=A{{e}^{x}}+B{{e}^{-x}}\] for different values of \[A\] and \[B\]

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

    B) \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=y\]

    C) \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=4y+3\]                   

    D) \[\frac{{{d}^{2}}y}{d{{x}^{2}}}+y=0\]

    Correct Answer: B

    Solution :

    Given curve is                 \[y=A{{e}^{x}}+B{{e}^{-x}}\]                                      ... (i) On differentiating w.r.t.,\[x,\] we get                 \[\frac{dy}{dx}=A{{e}^{x}}-B{{e}^{-x}}\] Again differentiating, we get                 \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=A{{e}^{x}}-B{{e}^{-x}}\] \[\Rightarrow \]               \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=y\]                           [from Eq.(i)]


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