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Math Help - Addition/Subtraction of Cosine

  1. #1
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    Addition/Subtraction of Cosine

    If I am using the addition and subtraction formula, how would I simplify cos(x + [pi])?
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  2. #2
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    Quote Originally Posted by mike1 View Post
    If I am using the addition and subtraction formula, how would I simplify cos(x + [pi])?
    cos(A + B) = cos(A)cos(B) - sin(A)sin(B)

    So
    cos(x + [pi]) = cos(x)cos([pi]) - sin(x)sin([pi])

    cos([pi]) = -1
    sin([pi]) = 0

    Thus
    cos(x + [pi]) = -cos(x)

    -Dan
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  3. #3
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    That helps, thanks alot.
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