JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Fundamental trigonometrical ratios and functions, Trigonometrical ratio of allied angles

  • question_answer
    If \[(1+\sin A)(1+\sin B)(1+\sin C)\]\[=(1-\sin A)(1-\sin B)(1-\sin C),\]then each side is equal to

    A) \[\pm \sin A\sin B\sin C\]

    B) \[\pm \cos A\cos B\cos C\]

    C) \[\pm \sin A\cos B\cos C\]

    D) \[\pm \cos A\sin B\sin C\]

    Correct Answer: B

    Solution :

    Multiplying both sides by \[(1-\sin A)(1-\sin B)(1-\sin C)\], we have, \[(1-{{\sin }^{2}}A)(1-{{\sin }^{2}}B)(1-{{\sin }^{2}}C)\]    \[={{(1-\sin A)}^{2}}{{(1-\sin B)}^{2}}{{(1-\sin C)}^{2}}\] Þ \[(1-\sin A)(1-\sin B)(1-\sin C)=\pm \cos A\cos B\cos C\] Similarly, \[(1+\sin A)(1+\sin B)(1+\sin C)=\pm \cos A\cos B\cos C\].


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