JEE Main & Advanced Sample Paper JEE Main Sample Paper-21

  • question_answer
    Suppose y is a function of x that satisfies \[\frac{dy}{dx}=\frac{\sqrt{1-{{y}^{2}}}}{{{x}^{2}}}\]and \[y=0\]at \[x=\frac{2}{\pi }\]then \[y\left( \frac{3}{\pi } \right)\]is  equal to

    A)  0                                

    B)  \[\frac{1}{2}\]

    C)  1                                

    D)  2

    Correct Answer: B

    Solution :

    \[\int_{{}}^{{}}{\frac{dy}{\sqrt{1-{{y}^{2}}}}\,=\int_{{}}^{{}}{\frac{dx}{{{x}^{2}}};}}\,\,\,{{\sin }^{-1}}y=\frac{-1}{x}+C\] \[y\left( \frac{2}{\pi } \right)=0\] gives \[C=\frac{\pi }{2}\] \[\therefore \,\,\frac{1}{x}\,=\frac{\pi }{2}\,-{{\sin }^{-1}}y={{\cos }^{-1}}(y)\] \[\Rightarrow \,y=\cos \left( \frac{1}{x} \right)\] \[\therefore \,y\left( \frac{3}{\pi } \right)=\cos \,\frac{\pi }{3}\,=\frac{1}{2}\]


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