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

  • question_answer
    If \[2x=\sec \theta \] and \[\frac{2}{x}=\tan \theta ,\] then \[2\left( {{x}^{2}}-\frac{1}{{{x}^{2}}} \right)=\]

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

    B) \[2\]

    C) \[\frac{1}{4}\]

    D) \[4\]

    Correct Answer: A

    Solution :

    [a] We have, \[2x=\sec \theta \] and \[\frac{2}{x}=\tan \theta \]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x=\frac{\sec \theta }{2}\] and \[\frac{1}{x}=\frac{\tan \theta }{2}\]….(1)
    \[\therefore \,\,\,\,\,\,\,\,\,\,2\left( {{x}^{2}}-\frac{1}{{{x}^{2}}} \right)=2\left( \frac{{{\sec }^{2}}\theta }{4}-\frac{{{\tan }^{2}}\theta }{4} \right)\] (From eq. (1))
    \[=\frac{2}{4}({{\sec }^{2}}\theta -{{\tan }^{2}}\theta )=\frac{1}{2}\cdot 1\] \[[{{\sec }^{2}}\theta -{{\tan }^{2}}\theta =1]\]


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