JEE Main & Advanced JEE Main Paper (Held On 25 April 2013)

  • question_answer
                    For\[0\le x\le \frac{\pi }{2},\] the value of\[\int\limits_{0}^{{{\sin }^{2}}x}{{{\sin }^{-1}}(\sqrt{t})\operatorname{dt}+}\int\limits_{0}^{{{\cos }^{2}}x}{{{\cos }^{-1}}(\sqrt{t})\operatorname{dt}}\]equals:     JEE Main Online Paper ( Held On 25  April 2013 )

    A) \[\frac{\pi }{4}\]                              

    B)                        0

    C)                        1                                             

    D)                        \[-\frac{\pi }{4}\]

    Correct Answer: A

    Solution :

                    Consider \[\int\limits_{0}^{{{\sin }^{2}}x}{{{\sin }^{-1}}(\sqrt{t})dt+\int\limits_{0}^{{{\cos }^{2}}x}{{{\cos }^{-1}}(\sqrt{t})dt}}\] Let \[I=f(x)\] after integrating and putting the limits. \[f'(x)={{\sin }^{-1}}\sqrt{{{\sin }^{2}}}x(2\sin x\cos x)-0\] \[+{{\cos }^{-1}}\sqrt{{{\cos }^{2}}x}(-2\cos x\sin x)-0\] \[\therefore \]\[f(x)=0\Rightarrow f(x)=C\](constant) Now, we find/(x) at \[x=\frac{\pi }{4}\] \[\therefore \]\[I=\int\limits_{0}^{1/2}{{{\sin }^{-1}}}\sqrt{t}dt+\int\limits_{0}^{1/2}{{{\cos }^{-1}}}\sqrt{t}dt\] \[=\int\limits_{0}^{1/2}{({{\sin }^{-1}}}\sqrt{t}+{{\cos }^{-1}}\sqrt{t})dt\] \[=\int\limits_{0}^{1/2}{\frac{\pi }{2}dt}=\frac{\pi }{4}=C\] \[\therefore \]\[f(x)=\frac{\pi }{4}\] \[\therefore \]Required integration = ?                


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