RAJASTHAN ­ PET Rajasthan PET Solved Paper-2001

  • question_answer
    If\[y=a{{x}^{n+1}}+b{{x}^{-n}},\]then\[\frac{{{x}^{2}}{{d}^{2}}y}{d{{x}^{2}}}\]is equal to

    A)  \[ny\]

    B)  \[{{n}^{2}}y\]

    C)  \[n(n-1)y\]

    D)  \[n(n+1)y\]

    Correct Answer: D

    Solution :

     \[y=a{{x}^{n+1}}+b{{x}^{-n}}\] \[\frac{dy}{dx}=(n+1)a{{x}^{n}}-bn{{x}^{-n-1}}\] \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=n(n+1)a{{x}^{n-1}}+n(n+1)b{{x}^{-n-2}}\] \[\Rightarrow \] \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=\frac{n(n+1)}{{{x}^{2}}}[a{{x}^{n+1}}+b{{x}^{-n}}]\] \[\Rightarrow \] \[{{x}^{2}}\frac{{{d}^{2}}y}{d{{x}^{2}}}=n(n+1)y\]


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