CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2006

  • question_answer
    \[y=-A\text{ }cos\text{ }5x+B\text{ }sin\text{ }5x\]satisfies the differential equation:

    A)  \[\frac{{{d}^{2}}y}{d{{x}^{2}}}+10\frac{dy}{dx}+25y=0\]

    B)  \[\frac{{{d}^{2}}y}{d{{x}^{2}}}-10\frac{dy}{dx}+25y=0\]

    C)  \[\frac{{{d}^{2}}y}{d{{x}^{2}}}-25y=0\]

    D)  \[\frac{{{d}^{2}}y}{d{{x}^{2}}}+25y=0\]

    E)  none of the above

    Correct Answer: D

    Solution :

    \[y=-A\cos 5x+B\sin 5x\] \[\frac{dy}{dx}=5A\sin 5x+5Bcos5x\] \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=25A\cos 5x-25B\sin 5x\] \[\Rightarrow \] \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=-25[-A\cos 5x+B\sin 5x]=-25y\] \[\Rightarrow \] \[\frac{{{d}^{2}}y}{d{{x}^{2}}}+25y=0\]


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