Posted by anonymous on Sunday, May 2, 2010 at 5:20pm.
I need help solving this problem algebraically, but I need to learn step by step!!
Thanks so much
cos 2x=cos x
How do I do it?

MATH ANALYSIS  Reiny, Sunday, May 2, 2010 at 5:42pm
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

MATH ANALYSIS  anonymous, Sunday, May 2, 2010 at 5:54pm
Thanks!
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