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    Question

    If cos4 B - sin4 B =

    src='https://static.ixambee.com/public/images/quesimg/Question Bank/Quantitative Aptitude/Trigonometry/86662_5358143.gif'> , then the value of 2 cos2 B - 1 is
    A 2/5 Correct Answer Incorrect Answer
    B 3/4 Correct Answer Incorrect Answer
    C 9/13 Correct Answer Incorrect Answer
    D √3 Correct Answer Incorrect Answer

    Solution

    cos4 B - sin4 B = (cos2 B + sin2 B)(cos2 B - sin2 B) = (cos2 B - sin2 B) = cos2 B - (1-cos2 B) = 2 cos2 B-1 =

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