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

  • question_answer
    The differential equation obtained on eliminating A and B from the equation \[y=A\cos \omega t+B\sin \omega t\] is [Karnataka CET 2000; Pb. CET 2001]

    A)                 \[{y}''=-{{\omega }^{2}}y\]            

    B)                 \[{y}''+y=0\]

    C)                 \[{y}''+{y}'=0\]   

    D)                 \[{y}''-{{\omega }^{2}}y=0\]

    Correct Answer: A

    Solution :

                       \[{y}'=-A\omega \sin \omega \,t+B\omega \cos \omega \,t\]         Again,\[{y}''=-A{{\omega }^{2}}\cos \omega \,t-B{{\omega }^{2}}\sin \omega \,t\]                       \[=\,-{{\omega }^{2}}(A\cos \omega \,t+B\sin \omega \,t)\].                 Therefore \[{y}''=-{{\omega }^{2}}y\].


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