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

  • question_answer
    If \[\tan \theta +\cot \theta =5,\] then the value of \[{{\tan }^{2}}\theta +{{\cot }^{2}}\theta \] is: (CBSE 2012)

    A) 1

    B) 7

    C) 23

    D) 25

    Correct Answer: C

    Solution :

    [c]Given, \[\tan \theta +\cot \theta =5\]
    Squaring on both sides, we get
    \[{{(\tan \theta +\cot \theta )}^{2}}={{(5)}^{2}}\]
    \[\Rightarrow \,\,\,\,\,\,{{\tan }^{2}}\theta +{{\cot }^{2}}\theta +2\tan \theta \cdot \cot \theta =25\]
    \[\Rightarrow \,\,\,\,\,\,{{\tan }^{2}}\theta +{{\cot }^{2}}\theta +2\tan \theta \cdot \frac{1}{\tan \theta }=25\]\[\left( \cot \theta =\frac{1}{\tan \theta } \right)\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,{{\tan }^{2}}\theta +{{\cot }^{2}}\theta =25-2\]
    \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{\tan }^{2}}\theta +{{\cot }^{2}}\theta =23\]


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