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Solve Trigonometric Equation

  1. Feb 21, 2009 #1
    Can anyone help solve the below for 'a'

    0=b(ycos(a)-bcos(2a)+xsin(a))

    I've reduced it to

    b=ycos(a)+2sin(a)sin(a)+xsin(a)

    =sin(a)(cot(a)+2sin(a)+x)

    Which I think is right, but I can't get any further without just ending up with different forms that appear more complex.
     
  2. jcsd
  3. Feb 21, 2009 #2

    Tom Mattson

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    What makes this equation tough is the fact that you've got 2 different trig functions running around there. What's more you've got 2 different arguments in your cosine functions. I would try to express everything in terms of [itex]\cos(a)[/itex], so that you end up with a polynomial equation in that quantity.

    Try to make use of the following identities:

    [tex]\cos(2a)=2\cos^2(a)-1[/tex]

    [tex]\sin(a)=\sqrt{1-\cos^2(a)}[/tex]

    I don't think you're going to get a closed form expression for a, but if you have numerical values for the parameters you will be able to get approximate solutions.
     
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