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JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Trigonometrical ratios of multiple and sub multiple angles

  • question_answer
    \[2{{\cos }^{2}}\theta -2{{\sin }^{2}}\theta =1\],then \[\theta \]= [Karnataka CET 1998]

    A) \[15{}^\circ \]

    B) \[30{}^\circ \]

    C) \[45{}^\circ \]

    D) \[60{}^\circ \]

    Correct Answer: B

    Solution :

    \[2{{\cos }^{2}}\theta -2{{\sin }^{2}}\theta =1\]Þ \[2\cos 2\theta =1\] Þ \[\cos 2\theta =\frac{1}{2}=\cos {{60}^{o}}\]Þ \[2\theta ={{60}^{o}}\Rightarrow \theta ={{30}^{o}}\].


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