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Math Help - trig identity help.

  1. #1
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    trig identity help.

    How do you prove ...

    sin(x+y)sin(x-y) = cos ^2y - cos ^2x

    1 + cos x = cot x / 2
    sin x

    tan(x+y)tan(x-y) = sin^2x - sin^2y / cos^2x -sin^2y

    (if anyone can tell me the math BBCode that would be nice too)
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  2. #2
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    Quote Originally Posted by finalfantasy View Post
    How do you prove ...

    sin(x+y)sin(x-y) = cos ^2y - cos ^2x
    Do you know the formula,
    \sin A \sin B now let A=x+y and B=x-y.
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  3. #3
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by finalfantasy View Post
    1 + cos x = cot x / 2
    sin x
    Hint: Multiply the top and bottom of the LHS by 1 - cos(x).

    -Dan
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