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Homework Help: Solving a trig equation for x

  1. Nov 6, 2011 #1
    1. The problem statement, all variables and given/known data
    cos^2x+2sin^2x=-1

    Solve for x

    2. Relevant equations



    3. The attempt at a solution
    I don't really know how to start. I know cos^2x+sin^2x=1 but I don't think I can apply that with the 2 thrown in there.
     
  2. jcsd
  3. Nov 6, 2011 #2

    SteamKing

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    Observe: cos^2 + 2 sin^2 = (cos^2 + sin^2) + sin^2
     
  4. Nov 6, 2011 #3
    thank you
     
  5. Nov 7, 2011 #4

    HallsofIvy

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    Or, if it weren't quite that obvious, you could have replaced [itex]cos^2(x)[/itex] with [itex]1- sin^2(x)[/itex]. That is, [itex]cos^2(x)+ 2sin^2(x)= (1- sin^2(x))+ 2sin^2(x)= 1+ sin^2(x)= 1.
     
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