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

  • question_answer
    The value \[\cos 105{}^\circ +\sin 105{}^\circ \]is [MNR 1975]

    A) \[\frac{1}{2}\]

    B) 1

    C) \[\sqrt{2}\]

    D) \[\frac{1}{\sqrt{2}}\]

    Correct Answer: D

    Solution :

    \[\cos 105{}^\circ +\sin 105{}^\circ =\cos (90{}^\circ +15{}^\circ )+\sin (90{}^\circ +15{}^\circ )\] =\[\cos 15{}^\circ -\sin 15{}^\circ =\frac{\sqrt{3}+1}{2\sqrt{2}}-\frac{\sqrt{3}-1}{2\sqrt{2}}=\frac{2}{2\sqrt{2}}=\frac{1}{\sqrt{2}}\].


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