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Math Help - sin(cosx)=0

  1. #1
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    sin(cosx)=0

    I need to prove sin(cosx)=0, but I'm looking through all of my identities and none of them seem to fit? Any help on this would be great!

    Thank you!
    Brittney
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  2. #2
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    Quote Originally Posted by Chinnie15 View Post
    I need to prove sin(cosx)=0, but I'm looking through all of my identities and none of them seem to fit? Any help on this would be great!

    Thank you!
    Brittney
    this equation is not true for all x (not an identity) ... it is a conditional equation, so there is nothing to "prove".

    since \sin(something) = 0 , then something has to be 0 or an integer multiple of \pi.

    since -1 \le \cos{x} \le 1 , none of the multiples of \pi will work, therefore \cos{x} can only equal 0.

    I leave you to determine those values of x that make \cos{x} = 0
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  3. #3
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    Oh ok, thanks! So if cos90=0.. that would get me my answer?
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  4. #4
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    Quote Originally Posted by Chinnie15 View Post
    Oh ok, thanks! So if cos90=0.. that would get me my answer?
    that would be one possible solution.
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  5. #5
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    Ok, I think I get it now. So cos of 270 is also equal to zero. And then all coterminal angles of 90 and 270?

    Edit: Here is my solution for my hw- Sin(cos x)=0 when x is 90360 or 270360. Sin(cos x)--> Sin(0) --> 0
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