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

  • question_answer
    If \[{{\tan }^{2}}A=1+2{{\tan }^{2}}B,\] then \[\frac{{{\cos }^{2}}A}{{{\cos }^{2}}B}=\]

    A) \[1\]

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

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

    D) \[\frac{\sqrt{3}}{2}\]

    Correct Answer: B

    Solution :

    [b] We have, \[{{\tan }^{2}}A=1+2{{\tan }^{2}}B\]
    \[\Rightarrow \,\,\,{{\sec }^{2}}A-1=1+2({{\sec }^{2}}B-1)\] \[[{{\tan }^{2}}\theta ={{\sec }^{2}}\theta =1]\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,{{\sec }^{2}}A=2+2{{\sec }^{2}}B-2\Rightarrow \,\,\,{{\sec }^{2}}A=2{{\sec }^{2}}B\]
    \[\Rightarrow \,\,\,\,\,\,\frac{1}{{{\cos }^{2}}A}=\frac{2}{{{\cos }^{2}}B}\,\,\,\,\,\,\,\,\,\,\,\Rightarrow \,\,\,\,\,\,\frac{{{\cos }^{2}}A}{{{\cos }^{2}}B}=\frac{1}{2}\]


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