RAJASTHAN ­ PET Rajasthan PET Solved Paper-2005

  • question_answer
    If\[{{y}^{2}}=a{{e}^{-2x}}+\frac{2}{5}(\cos x-2\sin x),\]then the value of\[y\frac{dy}{dx}+{{y}^{2}}+\sin x\] is

    A)  0              

    B)  \[-1\]

    C)  1              

    D)  None of these

    Correct Answer: A

    Solution :

     Given, \[{{y}^{2}}=a{{e}^{-2x}}+\frac{2}{5}(\cos x-2\sin x)\]   ...(i) On differentiating w.r.t.\[x,\]we get \[2y\frac{dy}{dx}=-2a{{e}^{-2a}}+\frac{2}{5}(-\sin x-2\cos x)\] \[\Rightarrow \] \[y\frac{dy}{dx}=-a{{e}^{-2x}}+\frac{1}{5}(-\sin x-2\cos x)\] \[\therefore \] \[y=\frac{dy}{dx}+{{y}^{2}}+\sin x\] \[=-a{{e}^{-2x}}+\frac{1}{5}(-\sin x-2\cos x)+a{{e}^{-2x}}\] \[+\frac{2}{5}(cox-2\sin x)+\sin x\] \[=-\frac{1}{5}\sin x-\frac{2}{5}\cos x+\frac{2}{5}\cos x-\frac{4}{5}\sin x\] \[+\sin x\] \[=0\]


You need to login to perform this action.
You will be redirected in 3 sec spinner