Pre Cal
posted by Kindell on .
2cos*2xcosx=1 find all solutions to the equation on the domain [0,2ð]
i got ð/4, 7ð/4, 3ð/4, and 5ð/4 but only got two out of four points... what did i do wrong?

Is cos*2x supposed to mean cos^2 x?
Is 2ð supposed to mean 2 pi?
If so,
2 cos^2x  cos x 1 = 0
which factors into
(2 cos x +1)(cos x 1) = 0
The solutions occur where cos x = 1/2 or +1
If cos*2x means cos(2x), then
2[2 cos^2 x 1)  cos x 1 = 0
4 cos^2 x cos x 3 = 0
(4 cosx +3)(cosx  1) = 0
x is where cos x = 3/4 or +1