JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Trigonometrical ratios of sum and difference of two and three angles

  • question_answer
    \[\frac{1}{\sin 10{}^\circ }-\frac{\sqrt{3}}{\cos 10{}^\circ }\]=     [IIT 1974]

    A) 0

    B) 1

    C) 2

    D) 4

    Correct Answer: D

    Solution :

    \[\frac{1}{\sin 10{}^\circ }-\frac{\sqrt{3}}{\cos 10{}^\circ }\] \[=\frac{2\,\left( \frac{1}{2}\cos {{10}^{o}}-\frac{\sqrt{3}}{2}\sin {{10}^{o}} \right)}{\frac{2}{2}\,\left( =\frac{\cos {{10}^{o}}-\sqrt{3}\sin {{10}^{o}}}{\sin {{10}^{o}}\cos {{10}^{o}}}\sin {{10}^{o}}\cos {{10}^{o}} \right)}\] \[=\frac{4\,\sin \,({{30}^{o}}-{{10}^{o}})}{\sin \,{{20}^{o}}}=\frac{4\,\sin \,{{20}^{o}}}{\sin \,{{20}^{o}}}=4\].


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