Manipal Engineering Manipal Engineering Solved Paper-2010

  • question_answer
    If\[y=\sin (m{{\sin }^{-1}}x)\], then\[(1-{{x}^{2}})y-xy\]is equal to

    A) \[{{m}^{2}}y\]                                  

    B) \[my\]

    C) \[-{{m}^{2}}y\] 

    D)         None of these

    Correct Answer: C

    Solution :

    We have,\[y=\sin (m{{\sin }^{-1}}x)\]                 \[\frac{dy}{dx}=\cos (m{{\sin }^{-1}}x).\frac{m}{\sqrt{1-{{x}^{2}}}}\] \[\Rightarrow \]\[(1-{{x}^{2}}){{\left( \frac{dy}{dx} \right)}^{2}}={{m}^{2}}{{\cos }^{2}}(m{{\sin }^{-1}}x)\]                 \[={{m}^{2}}(1-{{y}^{2}})\] On differentiating w.r.t.\[x\], again, we get                 \[(1-{{x}^{2}})2\cdot \frac{dy}{dx}\cdot \frac{{{d}^{2}}y}{d{{x}^{2}}}+{{\left( \frac{dy}{dx} \right)}^{2}}\cdot (-2x)\]                 \[=-2{{m}^{2}}y\frac{dy}{dx}\] \[\Rightarrow \]               \[(1-{{x}^{2}})\frac{{{d}^{2}}y}{d{{x}^{2}}}-x\frac{dy}{dx}=-{{m}^{2}}y\]                                             [\[\because \]Dividing by\[2dy/dx\]]


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