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18 July, 23:41

If sin (a) = cos (2a), then what is the value of a?

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  1. 19 July, 01:40
    0
    -90, 30

    Step-by-step explanation:

    sina = cos (2a)

    = 1 - 2 (sina) ^2

    2 (sina) ^2 + sina - - 1 = 0

    (sina + 1) (2sina - 1) = 0

    sina = - 1 or sina = 1/2

    => a = - 90 degrees or = > a = 30 degrees
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