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

  • question_answer
    If \[\tan x=\frac{b}{a},\]then \[\sqrt{\frac{a+b}{a-b}}+\sqrt{\frac{a-b}{a+b}}=\] [MP PET 1990, 2002]

    A) \[\frac{2\sin x}{\sqrt{\sin 2x}}\]

    B) \[\frac{2\cos x}{\sqrt{\cos 2x}}\]

    C) \[\frac{2\cos x}{\sqrt{\sin 2x}}\]

    D) \[\frac{2\sin x}{\sqrt{\cos 2x}}\]

    Correct Answer: B

    Solution :

    Given that, \[\tan x=\frac{b}{a}\] Now \[\sqrt{\frac{a+b}{a-b}}+\sqrt{\frac{a-b}{a+b}}=\sqrt{\frac{1+b/a}{1-b/a}}+\sqrt{\frac{1-b/a}{1+b/a}}\] \[=\frac{2}{\sqrt{1-\frac{{{b}^{2}}}{{{a}^{2}}}}}=\frac{2}{\sqrt{1-{{\tan }^{2}}x}}=\frac{2}{\sqrt{1-\frac{{{\sin }^{2}}x}{{{\cos }^{2}}x}}}=\frac{2\cos x}{\sqrt{\cos 2x}}\].


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