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    Question

    If cos2B = sin(1.5B + 20o), then find the

    measure of 'B'.
    A 16° 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 + 20°) Or, sin(90° - 2B) = sin(1.5B + 20°) Or, 90° - 2B = 1.5B + 20° Or, 2B + 1.5B = 90° - 20° So, 3.5B = 70° So, B = (70°/ 3.5) = 20° Hence, option c.

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