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

  • question_answer
    If \[\tan \theta =\frac{a\sin \phi }{1-a\cos \phi }\]and \[\tan \phi =\frac{b\sin \theta }{1-b\cos \theta },\]then \[\frac{a}{b}=\]

    A) \[\frac{\sin \theta }{1-\cos \theta }\]

    B) \[\frac{\sin \theta }{1-\cos \phi }\]

    C) \[\frac{\sin \phi }{\sin \theta }\]

    D) \[\frac{\sin \theta }{\sin \phi }\]

    Correct Answer: D

    Solution :

    [d] We have,\[\tan \theta =\frac{a\sin \phi }{1-a\cos \phi }\]
    \[\cot \theta =\frac{1}{a\sin \phi }-\cot \phi \]
    \[\cot \theta +\cot \phi =\frac{1}{a\sin \phi }\]……(1)
    \[\tan \phi =\frac{b\sin \theta }{1-b\cos \theta }\]
    \[\cot \theta =\frac{1}{b\sin \theta }-\cot \theta \]
    \[\cot \phi +\cot \theta =\frac{1}{b\sin \theta }\]
    From eqs. (1) and (2). we have
    \[\frac{1}{a\sin \phi }=\frac{1}{b\sin \theta }\]
    \[\frac{a}{b}=\frac{\sin \theta }{\sin \phi }\]


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