JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Mock Test - Trigonometric Functions

  • question_answer
    If A, B, C are angles of a triangle, then 2sin  \[\frac{A}{2}\cos ec\,\frac{B}{2}\sin \frac{C}{2}-\sin A\cot \frac{B}{2}-\cos A\]is

    A) independent of A, B,

    B) function of A, B

    C) function of C

    D)  none of these

    Correct Answer: A

    Solution :

    [a]      \[=\] \[2\sin \frac{A}{2}\cos ec\frac{B}{2}\left( \sin \frac{C}{2}-\cos \frac{A}{2}\cos \frac{B}{2} \right)-\cos A\] \[=2\sin \frac{A}{2}\cos ec\frac{B}{2}\times \left( \cos \frac{A+B}{2}-Cos\frac{A}{2}\cos \frac{B}{2} \right)-\cos A\] \[=\] \[2\sin \frac{A}{2}\cos ec\frac{B}{2}\times \left( -\sin \frac{A}{2}\sin \frac{B}{2} \right)-\cos A\] \[=-2{{\sin }^{2}}\frac{A}{2}-\cos A=-1\]


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