JEE Main & Advanced JEE Main Paper (Held on 08-4-2019 Morning)

  • question_answer
    \[\int_{{}}^{{}}{\frac{\sin \frac{5x}{2}}{\sin \frac{x}{2}}}dx\]is equal to: (where c is a constant of integration)               [JEE Main 8-4-2019 Morning]

    A) \[2x+sinx+2sin2x+c\]

    B) \[x+2sinx+2sin2x+c\]

    C) \[x+2sinx+sin2x+c\]

    D) \[2x+sinx+sin2x+c\]

    Correct Answer: C

    Solution :

    \[\int_{{}}^{{}}{\frac{\sin \frac{5x}{2}}{\sin \frac{x}{2}}}dx=\int_{{}}^{{}}{\frac{2\sin \frac{5x}{2}\cos \frac{x}{2}}{2\sin \frac{x}{2}\cos \frac{x}{2}}}dx\] \[=\int_{{}}^{{}}{\frac{\sin 3x+\sin 2x}{\operatorname{sinx}}}dx\] \[=\int_{{}}^{{}}{\frac{3\sin x-4{{\sin }^{3}}x-2\sin x\cos x}{\sin \,x}}dx\] \[=\int_{{}}^{{}}{(3-4{{\sin }^{2}}x+2cos\,x)\,}dx\] \[=\int_{{}}^{{}}{(3-2(1-cos2\,x)+2cos\,}x)dx\] \[=\int_{{}}^{{}}{(1+2cos2\,x+2cos\,}x)dx\] \[=x+\sin 2x+2\sin x+c\]


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