Question 755347
2 cosθ+1=- cos θ.
2 cos theta + 1 + cos theta = 0
3 cos theta + 1 = 0
 3 cos theta = -1
   cos theta = -1/3
Cos is negative in the second
and third quadrants
   theta = 1.9 and 4.4 radians
Hope this helps
:-)