Question

Find the solutions of the equation that are in the interval [0, 2pi). Cos u + cos 2u = 0

Answer 1

I can do the problem if I can set it up to a single cos function, which is what I have trouble doing.

Answer 2

Find the solutions of the equation in the interval [0,2∏)
cos(X/2)-sin(X)= 0
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cos(x/2) - 2sin(x/2)cos(x/2) = 0
cos(x/2) = 0
x/2 = 90, 270


x = 180º = pi (540 is 180, and exceeds 2pi)
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1 - 2sin(x/2) = 0
sin(x/2) = 1/2
x/2 = 30º, 150º
x = 60º, 300º = pi/3, 5pi/3