JEE Main & Advanced Mathematics Trigonometric Equations Question Bank Solution of trigonometrical equations

  • question_answer
    If cot \[(\alpha +\beta )=0,\]then \[\sin (\alpha +2\beta )=\]  [Kerala (Engg.) 2001]

    A) \[\sin \alpha \]

    B) \[\cos \alpha \]

    C) \[\sin \beta \]

    D) \[\cos 2\beta \]

    Correct Answer: A

    Solution :

    Given, cot \[(\alpha +\beta )=0\Rightarrow \cos (\alpha +\beta )=0\] Þ  \[\alpha +\beta =(2n+1)\frac{\pi }{2},n\in I\] \\[\sin (\alpha +2\beta )=\sin (2\alpha +2\beta -\alpha )\]=\[\sin \text{ }[(2n+1)\text{ }\pi -\alpha ]\]          \[=\sin (\,2n\pi +\pi -\alpha \,)\] = \[\sin (\,\pi -\alpha \,)\,=\sin \alpha \].


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