JEE Main & Advanced Mathematics Differential Equations Question Bank Formation of differential equations

  • question_answer
    \[y=4\sin 3x\]is a solution of the differential equation [AI CBSE 1986]

    A)                 \[\frac{dy}{dx}+8y=0\]     

    B)                 \[\frac{dy}{dx}-8y=0\]

    C)                 \[\frac{{{d}^{2}}y}{d{{x}^{2}}}+9y=0\] 

    D)                 \[\frac{{{d}^{2}}y}{d{{x}^{2}}}-9y=0\]

    Correct Answer: C

    Solution :

                       Let\[y=4\sin 3x\Rightarrow \frac{dy}{dx}=12\cos 3x\]         Þ \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=-36\sin 3x=-9\times 4\sin 3x=-9y\]                 Þ \[\frac{{{d}^{2}}y}{d{{x}^{2}}}+9y=0\].


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