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Stuck please help - 117.72=100sin2x + 28cosx

  1. Mar 26, 2014 #1
    Stuck please help -- 117.72=100sin2x + 28cosx

    Im trying to find an angle and im stuck

    117.72=100sin2x + 28cosx

    What do i do now?
  2. jcsd
  3. Mar 27, 2014 #2


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    You can always assume a value of x and evaluate the RHS of the equation to see if it equals the LHS.

    You can graph the RHS of the equation for different values of x, and then draw a line y= 117.72 and use the intersection points to estimate the values of x which are the solutions.

    You can use trig identities on the RHS to see if you obtain an equivalent expression in x which may be more amenable to solution.

    Take yer pick.
  4. Mar 27, 2014 #3
    use the identity (2cos(x)^2 -1) = sin2x to make it a quadratic equation with cosx instead of x
  5. Mar 27, 2014 #4
    (2cos(x)^2 -1) = sin2x

    Thats a trig Identity?
  6. Mar 27, 2014 #5
    ah my memory was bad that one is for cos2x sorry
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