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

  • question_answer
    \[\sqrt{-4+\sqrt{8+16\,\text{cose}{{\text{c}}^{4}}\theta +{{\sin }^{4}}\theta }}=A\,\text{cosec}\theta \text{+Bsin}\theta \text{,}\] then A and B are:

    A) \[2\] and \[-1\]

    B) \[1\]and \[\frac{1}{2}\]

    C) \[\frac{1}{2}\]and \[\frac{1}{3}\]

    D) \[3\] and \[-4\]

    Correct Answer: A

    Solution :

    [a] \[\sqrt{-4+\sqrt{8+16\cos e{{c}^{4}}\theta +{{\sin }^{4}}\theta }}\]
    \[=\sqrt{-4+\sqrt{8+\frac{16}{{{\sin }^{4}}\theta }+{{\sin }^{4}}\theta }}\]]
    \[=\sqrt{-4+\sqrt{{{\left( \frac{4}{{{\sin }^{2}}\theta }+{{\sin }^{2}}\theta  \right)}^{2}}}}\]
    \[[{{a}^{2}}+2ab+{{b}^{2}}={{(a+b)}^{2}}]\]
    \[=\sqrt{-4+\frac{4}{{{\sin }^{2}}\theta }+{{\sin }^{2}}\theta }\]\[[{{a}^{2}}-2ab+{{b}^{2}}={{(a-b)}^{2}}]\]
    \[=\sqrt{{{\left( -\sin \theta +\frac{2}{\sin \theta } \right)}^{2}}}=2\cos ec\,\theta (-1)\sin \theta \]
    \[=A\,\,\cos ec\,\,\theta +B\sin \theta \]
    On comparing, we get
    \[A=2\]  and \[B=-1\]


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