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

  • question_answer
    \[(1+\tan \theta +\sec \theta )\,\,(1+\cot \theta -\text{cosec }\theta \text{)}\] is equal to:        (NCERT EXEMPLAR)

    A) 0

    B) 1

    C) 2

    D) -1

    Correct Answer: C

    Solution :

    [c]\[(1+\tan \theta +\sec \theta )(1+\cot \theta -\cos ec\theta )\]
    \[=\left\{ 1+\frac{\sin \theta }{\cos \theta }+\frac{1}{\cos \theta } \right\}\,\,\,\,\left\{ 1+\frac{\cos \theta }{\sin \theta }-\frac{1}{\sin \theta } \right\}\]
    \[=\frac{\sin \theta +\cos \theta +1}{\cos \theta }\times \frac{\sin \theta +\cos \theta -1}{\sin \theta }\]
    \[[(a+b)\,\,(a-b)={{a}^{2}}-{{b}^{2}}]\]
    \[=\frac{{{(\sin \theta +\cos \theta )}^{2}}-1}{\sin \theta \cdot \cos \theta }=\frac{{{\sin }^{2}}\theta +{{\cos }^{2}}\theta +2\sin \theta \cdot \cos \theta -1}{\sin \theta \cdot \cos \theta }\]
    \[=\frac{1+2\sin \theta \cdot \cos \theta -1}{\sin \theta \cdot \cos \theta }=\frac{2\sin \theta \cdot \cos \theta }{\sin \theta \cdot \cos \theta }=2\]
    \[[{{\sin }^{2}}\theta +{{\cos }^{2}}\theta =1]\]


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