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Given sinx=4/5, cosy = 7/25. Find the following

  1. Feb 10, 2009 #1
    1. The problem statement, all variables and given/known data

    Angles x and y are located in the first quadrant such that sinx=4/5, and cosy = 7/25.

    a) Determine an exact value of cosx.

    b) Determine an exact value of siny.

    c) Determine an exact value for sin(x+y)

    2. Relevant equations

    Compound angle formulas perhaps? I don't really know, thats the problem!

    3. The attempt at a solution

    I'm really at a loss here, do I just sub those in to some formula or something? Can anyone help me out? Or get me pointed in the right direction? thanks in advance!!
  2. jcsd
  3. Feb 10, 2009 #2
    Let's start with part a). Have you thought about [tex] sin^2(x) + cos^2(x) = 1 [/tex]?
  4. Feb 10, 2009 #3
    Holy smoke I can't believe I missed that! thanks hitman! I owe you one!

    Now for the last 2 lil buggers!
  5. Feb 10, 2009 #4
    well I got a and b, now how would I do c? :|
  6. Feb 10, 2009 #5
    Nevermind, I got it, thanks for your help hitman! I don't know how on earth i missed that!!
  7. Feb 10, 2009 #6
    sin(x+y) = sinx*cosy+siny*cosx
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