Find Radian Angle: Value of cos θ = -1/2, π ≤ θ ≤ 2π

[Veronica_Oles]

Homework Statement

For the value of cos θ, determine the radian value of θ if π ≤ θ ≤ 2π.

Value is -1/2.

Homework Equations

The Attempt at a Solution

I got the first value which is cos^-1(-1/2) which I got (2π)/3.
However I am unsure how to get the second value.
I thought that since the first value is in second quadrant the other value is in the third quadrant, then I would take θ-π to find my value in the quadrant. But my answer was incorrect. Can someone pls guide me? Thx.

 

[Mark44]

Homework Statement

For the value of cos θ, determine the radian value of θ if π ≤ θ ≤ 2π.

Value is -1/2.

Homework Equations

The Attempt at a Solution

I got the first value which is cos^-1(-1/2) which I got (2π)/3.
However I am unsure how to get the second value.
I thought that since the first value is in second quadrant the other value is in the third quadrant, then I would take θ-π to find my value in the quadrant. But my answer was incorrect. Can someone pls guide me? Thx.

What angle in the 3rd quadrant has a cosine of -1/2? Draw a unit circle and use basic geometry to find that angle.