10th Class Mathematics Introduction to Trigonometry Question Bank MCQs - Introduction to Trigonometry

  • question_answer
    If \[\tan \theta +\sin \theta =m\] and \[\tan \theta -\sin \theta =n,\] then \[{{m}^{2}}-{{n}^{2}}\] is equal to:

    A) \[\sqrt{mn}\]

    B) \[\sqrt{\frac{m}{n}}\]

    C) \[4\sqrt{mn}\]

    D) None of these

    Correct Answer: C

    Solution :

    [c] Given, \[\tan \theta +\sin \theta =m\]and \[\tan \theta -\sin \theta =n\]
    \[{{m}^{2}}-{{n}^{2}}={{(\tan \theta +\sin \theta )}^{2}}-{{(\tan \theta -\sin \theta )}^{2}}\]
    \[=4\tan \theta \sin \theta =4\sqrt{{{\tan }^{2}}\theta {{\sin }^{2}}\theta }\]
    \[=4\sqrt{{{\sin }^{2}}\theta \frac{{{\sin }^{2}}\theta }{{{\cos }^{2}}\theta }}=4\sqrt{\frac{{{\sin }^{2}}\theta }{{{\cos }^{2}}\theta }-{{\sin }^{2}}\theta }\]
    \[=4\sqrt{{{\tan }^{2}}\theta -{{\sin }^{2}}\theta }\]
    \[=4\sqrt{(\tan \theta +\sin \theta )\,(\tan \theta -\sin \theta )}=4\sqrt{mn}\]


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