Question

Trig help?
Find all solutions to the equation in the interval [0, 2π).

cos 2x - cos x = 0

Answer 1

cos 2x = 2sinxcosx
By factorizing cos x out:
cos 2x - cos x = 0
2sinxcosx - cosx = 0
(cosx)(2sinx-1) = 0

Solve for:
cosx = 0 AND 2sinx -1 = 0
x=??? AND sinx = 1/2
x=??? AND x2=???

Find which are the common solutions, that will be your answer.

Answer 2

thats wrong... you have to use cos2x=2(cosx)^2-1

sin2x=2sinxcosx....not cos2x

Answer 3

yeah o.o