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Math Help - derving trig equations

  1. #1
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    derving trig equations

    with these identities

    a. sin(-x) = -sinx
    b. cos(-x) = cos(x)
    c. cos(x+y) = cosxcosy - sinxsiny
    d. sin(x+y) = sinxcosy + cosxsiny

    i need to derive this

    sin^2x + cos^2x = 1


    can anyone help me
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  2. #2
    MHF Contributor

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    With the following can you complete it?
    1 = \cos (0) = \cos \left( {x + ( - x)} \right) = \cos (x)\cos ( - x) - \sin (x)\sin ( - x)
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