Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    \[\cos A\cos 2A\cos 4A...\cos {{2}^{n-1}}A\]equals

    A) \[\frac{\sin {{2}^{n}}A}{{{2}^{n}}\sin A}\]                             

    B) \[\frac{{{2}^{n}}\sin {{2}^{n}}A}{\sin A}\]

    C) \[\frac{{{2}^{n}}\sin A}{\sin {{2}^{n}}A}\]             

    D)        \[\frac{\sin A}{{{2}^{n}}\sin {{2}^{n}}A}\]

    Correct Answer: A

    Solution :

    It is a standard result.                 \[\cos A\cos 2A\cos {{2}^{2}}A...\cos {{2}^{n-1}}A\]                 \[=\frac{\sin {{2}^{n}}A}{{{2}^{n}}\sin A}\]


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