JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Trigonometrical ratios of multiple and sub multiple angles

  • question_answer
    For \[A=133{}^\circ ,\ 2\cos \frac{A}{2}\]is equal to [DCE 2001]

    A) \[-\sqrt{1+\sin A}-\sqrt{1-\sin A}\]

    B)   \[-\sqrt{1+\sin A}+\sqrt{1-\sin A}\]

    C) \[\sqrt{1+\sin A}-\sqrt{1-\sin A}\]

    D) \[\sqrt{1+\sin A}+\sqrt{1-\sin A}\]

    Correct Answer: C

    Solution :

    For \[A={{133}^{o}},\frac{A}{2}={{66.5}^{o}}\] Þ  \[\sin \frac{A}{2}>\cos \frac{A}{2}>0\] Hence\[\sqrt{1+\sin A}=\sin \frac{A}{2}+\cos \frac{A}{2}\] ?..(i) and \[\sqrt{1-\sin A}=\sin \frac{A}{2}-\cos \frac{A}{2}\] ?..(ii) Subtract (ii) from (i), \[2\cos \frac{A}{2}=\sqrt{1+\sin A}-\sqrt{1-\sin A}\].


You need to login to perform this action.
You will be redirected in 3 sec spinner