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    Question

    If Sin x + Sin2x = 1, then what is the value

    of Cos8x + 2cos6x + Cos4x?
    A 2 Correct Answer Incorrect Answer
    C 4 Correct Answer Incorrect Answer
    D 1 Correct Answer Incorrect Answer

    Solution

    Sin x + Sin2x = 1 Sinx=1-Sin2x =cos2x Sinx =cos2x    ...(1) Sin x + Sin2x = 1  ...(2) both sides squaring. (Sin x + Sin2x)2 = (1)2 sin2x+sin4 x+2.sinx.sin2x =1 sin2x+sin4x+2.sin3 x =1 now put the value of sinx from Eq (1).. Cos8x + 2cos6x + Cos4x =1

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