JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Fundamental Integration

  • question_answer
    If \[\int_{{}}^{{}}{\frac{dx}{1+\sin x}=\tan \left( \frac{x}{2}+a \right)+b}\], then [Roorkee 1979]

    A)            \[a=\frac{\pi }{4},\ b=3\]         

    B)            \[a=-\frac{\pi }{4},\ b=3\]

    C)            \[a=\frac{\pi }{4},\ b=\]arbitrary constant                                  

    D)            \[a=-\frac{\pi }{4},\ b=\]arbitrary constant

    Correct Answer: D

    Solution :

               \[\int_{{}}^{{}}{\frac{dx}{1+\sin x}}=\tan x-\sec x+c=-\frac{1-\sin x}{\cos x}\]                          \[=-\frac{{{\left( \cos \frac{x}{2}-\sin \frac{x}{2} \right)}^{2}}}{{{\cos }^{2}}\frac{x}{2}-{{\sin }^{2}}\frac{x}{2}}+c=-\frac{1-\tan \frac{x}{2}}{1+\tan \frac{x}{2}}+c\]                          \[=\frac{\tan \frac{x}{2}-1}{1+\tan \frac{x}{2}}+c=\tan \left( \frac{x}{2}-\frac{\pi }{4} \right)+c\]            \[\Rightarrow a=-\frac{\pi }{4},\,\,b=\] arbitrary constant.


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