Math Help - Trigonometric Equation

1. Trigonometric Equation

Solve the trig equation..

1-9*cos^2 (2x) = 0

My Work:

1-9*cos^2 (2x)
cos^2 (2x) =1/9
cos (2x) =1/3 or -1/3
2x=arccos(1/3)
x=0.5*arccos(1/3)
or
2x=arccos(-1/3)
x=0.5*arccos(-1/3)

Is this correct? When I plug the value of x into the given trig equation, I do not get 0 = 0.

2. Re: Trigonometric Equation

seems right to me

3. Re: Trigonometric Equation

what you've done is correct but not complete. There are actually 8 solutions between 0 and 2pi and of course there are an infinite number of solutions overall.