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

  • question_answer
    If \[\frac{1}{1+\sin \theta }+\frac{1}{1-\sin \theta }=k{{\sec }^{2}}\theta ,\] then the value of k is:

    A) \[1\]

    B) \[-1\]

    C) \[2\]

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

    Correct Answer: C

    Solution :

    [c]\[\frac{1}{1+\sin \theta }+\frac{1}{1-\sin \theta }=\frac{1-\sin \theta +1+\sin \theta }{(1+\sin \theta )(1-\sin \theta )}\]
    \[[{{\sin }^{2}}+{{\cos }^{2}}\theta =1]\]
    \[=\frac{2}{1-{{\sin }^{2}}\theta }=\frac{2}{{{\cos }^{2}}\theta }=2{{\sec }^{2}}\theta =k{{\sec }^{2}}\theta \]
    On Comparing we get  k=2


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