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

  • question_answer
    If \[\tan \theta +\sin \theta =m\]and \[\tan \theta -\sin \theta =n,\]then [IIT 1970]

    A) \[{{m}^{2}}-{{n}^{2}}=4mn\]

    B) \[{{m}^{2}}+{{n}^{2}}=4mn\]

    C) \[{{m}^{2}}-{{n}^{2}}={{m}^{2}}+{{n}^{2}}\]

    D) \[{{m}^{2}}-{{n}^{2}}=4\sqrt{mn}\]

    Correct Answer: D

    Solution :

    \[(m+n)=2\,\tan \theta ,\,\,m-n=2\,\sin \theta \] \[\therefore \,\,\,{{m}^{2}}-{{n}^{2}}=4\,\tan \theta \,.\,\sin \theta \] ?..(i) \[4\sqrt{mn}=4\sqrt{{{\tan }^{2}}\theta -{{\sin }^{2}}\theta }=4\,\sin \theta \,.\,\tan \theta \] ?..(ii) From (i) and (ii), \[{{m}^{2}}-{{n}^{2}}=4\sqrt{mn}\].


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