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    wazhma1991's Avatar
    wazhma1991 Posts: 8, Reputation: 1
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    #1

    Mar 15, 2009, 07:05 AM
    Trigonometry
    sin(-2A)=-2sinAcos(-A)
    Perito's Avatar
    Perito Posts: 3,139, Reputation: 150
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    #2

    Mar 16, 2009, 04:42 AM

    First, start by proving

    sin (x + y) = sin(x) cos(y) + cos(x) sin (y)

    sin(x+y) and cos(x+y)

    Then simplify by letting x = y to the traditional double-angle formula:

    Finally, substitute -A for x and you'll have your proof.
    wazhma1991's Avatar
    wazhma1991 Posts: 8, Reputation: 1
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    #3

    Mar 22, 2009, 04:49 AM
    Hi how you solved?:confused:
    wazhma1991's Avatar
    wazhma1991 Posts: 8, Reputation: 1
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    #4

    Mar 22, 2009, 04:55 AM
    Thanks
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