Solve the equation 2 cos x + 1 = 0 , 0 < = x < = 2pi ! will award!

It would be pi over 6, 5 pi over 6, and 3 pi over 6.

Im not saying its right but I got 0,2π3,4π3,and2π  f(x)=2cos2x−cosx−1=0
Solve this quadratic equation for cos x.
Since a + b + c = 0, use shortcut.
One real root is cos x = 1 and the other is cosx=ca=−12.
Trig table and unit circle -->
a. cos x = 1 --> arc x = 0, and arc x=2π
b. cosx=−12 --> arc x=±2π3
The arc −2π3 is co-terminal to the arc: 4π3
Answers for (0,2π):
0,2π3,4π3,and2π