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Math Help - Sine and Cosine

  1. #1
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    Sine and Cosine

    Not sure what this question is asking me, when their is no numbers to calculate, can someone please explain this to me

    If Cos(x)=m then what is the value of Cos (180-x)?

    Thanks
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  2. #2
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    \cos(a-b) = \cos a \cos b + \sin a \sin b
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  3. #3
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    It's a trigonometric identity.

    cos(180 - x) is always the opposite of cos(x).

    You could come to that conclusion several ways, but the easiest method is to look at a typical angle Q on a graph and compare it with its supplement (which is defined as 180 - Q), and then you will see why the conclusion is true.
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  4. #4
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    Quote Originally Posted by icemanfan View Post
    It's a trigonometric identity.

    cos(180 - x) is always the opposite of cos(x).

    You could come to that conclusion several ways, but the easiest method is to look at a typical angle Q on a graph and compare it with its supplement (which is defined as 180 - Q), and then you will see why the conclusion is true.
    so the answer that i would be looking for then is -cos(180-x), or am i way out to lunch on this one
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  5. #5
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    Quote Originally Posted by nuckers View Post
    so the answer that i would be looking for then is -cos(180-x), or am i way out to lunch on this one
    Well, if cos(x) = m and cos(180 - x) is the opposite of cos(x), then what does cos(180 - x) equal in terms of m?
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  6. #6
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    Quote Originally Posted by nuckers View Post
    so the answer that i would be looking for then is -cos(180-x), or am i way out to lunch on this one
    if \cos{x} = m , then \cos(180-x) = -m

    ... that's all.
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  7. #7
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    Quote Originally Posted by icemanfan View Post
    Well, if cos(x) = m and cos(180 - x) is the opposite of cos(x), then what does cos(180 - x) equal in terms of m?
    Ok, i understand now, thanks so much for the help
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