SOLUTION: Solve 2cos x+2cos 2x=0 on the interval [0,2pi)

Algebra ->  Trigonometry-basics -> SOLUTION: Solve 2cos x+2cos 2x=0 on the interval [0,2pi)      Log On


   

Question 484085: Solve 2cos x+2cos 2x=0 on the interval [0,2pi)
Answer by Joker(6) About Me  (Show Source):
You can put this solution on YOUR website!
First use the double angle formula to get 2cos x+2(2cos^2 x-1)=0 then distribute and simplify by dividing by 2 to get 2cos^2 x+cos x-1=0 then factor into (2cos x-1)(cos x+1)=0 and solve for x using the unit circle where cos x = 1/2 and -1 which is at pi/3,5pi/3 and pi.