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

  • question_answer
    If \[\cos \alpha =\frac{\sqrt{3}}{2}\]and \[\tan \beta =\frac{1}{\sqrt{3}},\]then the value of \[\sin (\alpha +\beta ),\] where \[\alpha \]and \[\beta \]both are acute angles is:

    A) \[\frac{1}{2}+\frac{1}{\sqrt{3}}\]

    B) \[\sqrt{3}+2\]

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

    D) \[0\]

    Correct Answer: C

    Solution :

    [c] We have, \[\cos \alpha =\sqrt{3}/2\,\,\Rightarrow \alpha =30{}^\circ \] \[[\cos 30{}^\circ =\sqrt{3}/2]\]
    and  \[\tan \beta =\frac{1}{\sqrt{3}}\,\,\,\,\,\,\,\,\,\,\Rightarrow \,\,\,\,\,\beta =30{}^\circ \] \[\left[ \tan 30{}^\circ =\frac{1}{\sqrt{3}} \right]\]
    \[\therefore \,\,\,\,\,\,\,\,\,\,\alpha +\beta =30{}^\circ +30{}^\circ =60{}^\circ \]
    \[\therefore \,\,\,\,\,\,\,\,\,\,\sin (\alpha +\beta )=\sin 60{}^\circ =\frac{\sqrt{3}}{2}\]


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