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    Question

    If cos2B = sin(1.5B + 6°), then find the measure of

    'B'.
    A 24° Correct Answer Incorrect Answer
    B 18° Correct Answer Incorrect Answer
    C 20° Correct Answer Incorrect Answer
    D 22° Correct Answer Incorrect Answer

    Solution

    We know that, cosA = sin(90° - A) cos2B = sin(1.5B + 6°) Or, sin(90° - 2B) = sin(1.5B + 6°) Or, 90° - 2B = 1.5B + 6° Or, 2B + 1.5B = 90° - 6° So, 3.5B = 84° So, B = (84°/ 3.5) = 24° Hence, option d. 

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