JEE Main & Advanced Sample Paper JEE Main - Mock Test - 11

  • question_answer
    If \[y(x)\] satisfies the equation \[x\sin y+x=y,\] then the value of \[y''(\pi )=\]

    A) \[-\frac{1}{{{(\pi +1)}^{2}}}\] 

    B) \[-\frac{2}{{{(\pi +1)}^{2}}}\]

    C) \[-\frac{1}{\pi +1}\]      

    D) \[\frac{2}{\pi +1}\]

    Correct Answer: B

    Solution :

    [b] \[x\text{ }sin\text{ }y+x=y\] Differentiating w.r.t. x, we get \[x(\cos y)y'+\sin y+1=y'\]                          ...(1) When \[x=\pi \] then \[y=\pi \]. Putting these values into (1), we get \[\pi (-1)y'+0+1=y'\] \[\Rightarrow \,\,\,y'(\pi )=\frac{1}{\pi +1}\] Differentiating (1) w.r.t. x, we get \[(\cos \,\,y)'-x(\sin y){{(y')}^{2}}+x(\cos \,y)y''+(\cos y)y'=y''\]  ...(2) Putting \[x=\pi \] and \[y=\pi \] into (2), we get \[-\frac{1}{\pi +1}-0-\pi y''-\frac{1}{\pi +1}=y''\] \[\Rightarrow \,\,y''\left( 1+\pi  \right)=-\frac{2}{{{\left( \pi +1 \right)}^{2}}}\]


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