SOLUTION: I'm having trouble solving this equation: sin2theta = cos36 degrees. I have tried to use the double angle formula for sin2theta and split it into 2sintheta times costheta and end u

Question 642030: I'm having trouble solving this equation: sin2theta = cos36 degrees. I have tried to use the double angle formula for sin2theta and split it into 2sintheta times costheta and end up getting 2sintheta times costheta = cos36 degrees, but I don't know what to do from there to get it to become a single trig function so that I can solve for theta.
Answer by DrBeeee(684) (Show Source): You can put this solution on YOUR website!
The trig ID you need to use is
(1) cos(x) = sin(90-x)
Then your
(2) cos(36) = sin(90-36) or
(3) cos(36) = sin(54)
Now you have
(4) sin(2*A) = sin(54) or
(5) 2*A = 54 or
(6) A = 27
Answer: Theta is 27 degrees
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