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

  • question_answer
    In \[\Delta ABC,\] \[\angle B=90{}^\circ \]. If \[\tan A=\sqrt{3},\]then the value of \[\sin A.\cos C-\cos A.\sin C\] is:

    A) \[\frac{1}{2}\]

    B) \[-1\]

    C) \[1\]

    D) \[0\]

    Correct Answer: A

    Solution :

    [a] We have,  \[A=\sqrt{3}\]
    \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\angle A=60{}^\circ \]  \[[\tan 60{}^\circ =\sqrt{3}]\]
    \[\Rightarrow \,\,\,\,\,\,\,\angle C=180{}^\circ -90{}^\circ -\angle A=90{}^\circ -60{}^\circ =30{}^\circ \]
    \[\therefore \,\,\,\,\,\,\,\,\sin A\cdot \cos C-\cos A\cdot \sin C\]
    \[=\sin 60{}^\circ \cdot \cos 30{}^\circ -\cos 60{}^\circ \cdot \sin 30{}^\circ \]
    \[=\frac{\sqrt{3}}{2}\times \frac{\sqrt{3}}{2}-\frac{1}{2}\times \frac{1}{2}=\frac{3}{4}-\frac{1}{4}=\frac{2}{4}=\frac{1}{2}\]


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