Answer:
θ = 2π/3 or 5π/3
Step-by-step explanation:
2 cosθ + 1= 0
when + 1 goes to R H S Side than it becomes negative by transposition method
2 cos = -1
now by dividing by 2 both sides we get
cosθ = -
since cosθ is negative
Cosθ = - cos 60°
it means either cosθ lies in 2nd or third quadrant
θ = π - π/3
or
θ = 2π- π/3
so θ = 2π/3 or 5π/3