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Trig homework help

  1. Apr 15, 2012 #1
    1. The problem statement, all variables and given/known data

    If Sin(u)=[itex]\frac{\sqrt{2}}{2}[/itex] and cos(v)=[itex]\frac{4}{5}[/itex] and

    0≤ u ≤[itex]\frac{∏}{2}[/itex] and [itex]\frac{3∏}{2}[/itex]≤ v ≤ 2∏

    find cos (u+v)



    3. The attempt at a solution

    cos(u)=[itex]\frac{\sqrt{2}}{2}[/itex] and cos(v)=[itex]\frac{4}{5}[/itex]

    Do I just add them together? I feel like I'm missing something, but maybe the problem really is that simple.
     
  2. jcsd
  3. Apr 15, 2012 #2

    SammyS

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    Re: Trig

    Use the angle addition identity for cosine .
     
  4. Apr 15, 2012 #3
    Re: Trig

    So it would be..

    ([itex]\frac{\sqrt{2}}{2}[/itex])([itex]\frac{4}{5}[/itex])-([itex]\frac{\sqrt{2}}{2}[/itex])([itex]\frac{-3}{5}[/itex]) = [itex]\frac{7\sqrt{2}}{10}[/itex]
     
  5. Apr 16, 2012 #4

    ehild

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    Re: Trig

    Excellent!

    ehild
     
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