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Homework Help: Trig functions, finding co-ordinates

  1. Sep 24, 2012 #1
    1. The problem statement, all variables and given/known data

    I have a graph with the functions f(x)=sin2x and g(x)=cosx. The 2 graphs intersect at point B. They want me to find the co-ordinates of B.

    2. Relevant equations

    3. The attempt at a solution

    Must I equate the two graphs?

    sin2x = cosx
    2x = 90-x, 3x = 90, x=30 or 2x = 180-(90-x), x=90

    It doesnt seem right, is their any other steps?
  2. jcsd
  3. Sep 24, 2012 #2
    Aren't you given any specific range within which you want the solution, both the graphs intersect at many points.
  4. Sep 24, 2012 #3
    they say that f and g intersect at A(30:0.87) and B.
    the domain is xE[0;270].
    Thats all that is given.
  5. Sep 24, 2012 #4


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    Do you know a trig identity for sin(2x)?
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