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

  • question_answer
    \[\frac{\sin \theta }{(1-\cot \theta )}+\frac{\cos \theta }{(1-\tan \theta )}\] is equal to:

    A) \[(\cos \theta +\sin \theta )\]

    B) \[(\cos \theta -\sin \theta )\]

    C) \[0\]

    D) \[2\tan \theta \]

    Correct Answer: A

    Solution :

    [a] We have,  \[\frac{\sin \theta }{(1-\cot \theta )}+\frac{\cos \theta }{(1-\tan \theta )}\]
    \[=\frac{\sin \theta }{\left( 1-\frac{\cos \theta }{\sin \theta } \right)}+\frac{\cos \theta }{\left( 1-\frac{\sin \theta }{\cos \theta } \right)}=\frac{{{\sin }^{2}}\theta }{(\sin \theta -\cos \theta )}+\frac{{{\cos }^{2}}\theta }{(\cos \theta -\sin \theta )}\]
    \[=\frac{{{\cos }^{2}}\theta }{(\cos \theta -\sin \theta )}-\frac{{{\sin }^{2}}\theta }{(\cos \theta -\sin \theta )}=\frac{({{\cos }^{2}}\theta -{{\sin }^{2}}\theta )}{(\cos \theta -\sin \theta )}\]
    \[=\frac{(\cos \theta -\sin \theta )(\cos \theta +\sin \theta )}{(\cos \theta -\sin \theta )}=\cos \theta +\sin \theta \]


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