Posted by anonymous on Sunday, May 2, 2010 at 5:20pm.
you should know that
cos 2x = 2cos^2 x - 1
so we have
2cos^2 x - 1 = cosx
2cos^2 x - cosx - 1 = 0
(2cosx + 1)(cosx -1) = 0
cosx = -1/2 or cosx = 1
x = 120° or 240° or x = 0 or 360
in radians
x = 0, 2π/3, 4π/3, 2π
Thanks!
Thanks!
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