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Math Help - Trig with a domain.

  1. #1
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    Trig with a domain.

    I have a question that's restricted to a certain domain (I guess). Obviously I only give the answers that fall in there. The question goes like this:

    0 < theta < pi/2 So I know it's between 0-90 degrees.

    I have cos(theta) = 3/5

    I have to find sin(2theta) which is 2sin(theta)cos(theta) so my little cheat sheet says. Do I just fill in 3/5 to that equation? It seems easy enough I guess. I am just confirming what I am doing is actually right. Thanks a million in advance.
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  2. #2
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    yes, you'll substitute 3/5 for the cosine value, but what about the value for sine?
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  3. #3
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    So there's probably another equation for it isn't there?
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  4. #4
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    sketch a reference triangle in quad I. you know the ratio of the adjacent side over the hypotenuse = 3/5

    so, what is the ratio of the opposite side over the hypotenuse for the same triangle?
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  5. #5
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    Does this mean the r value = 5 and y = 3??
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  6. #6
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    Quote Originally Posted by cjh824 View Post
    Does this mean the r value = 5 and y = 3??
    r = 5 and x = 3

    y = ?
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