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Math Help - proving an identity

  1. #1
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    proving an identity

    prove that

    2sin2a - 3cos2a - 3sina + 3 = sina(4cosa + 6sina - 3)

    i am very tired and cant seem to figure it out. would be grateful for any help.
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  2. #2
    Moo
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    Hello,

    sin(2a)=2cos(a)sin(a)
    cos(2a)=cosē(a)-sinē(a)=(1-sinē(a))-sinē(a)=1-2sinē(a)

    If you replace these values in the initial expression, you'll get what you want ;-)
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