SOLUTION: cos 2x + cos x = 0

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Question 751524: cos 2x + cos x = 0
Answer by Cromlix(4381) About Me  (Show Source):
You can put this solution on YOUR website!
cos2x + cos x
replace cos 2x with 2cos^2-1
2cos^2-1 + cos x = 0
Rearrange
2cos^2x + cos x - 1 = 0
(2cosx - 1)(cosx + 1) = 0
cosx = 1/2 or -1

x = 60 degs, 300degs and 180degs
= pi/3 rads, 5pi/3 rads and pi