The co-ordinates of a point on the unit circle are `(-sqrt 3/2, -1/2)` . The terminal side of angle theta in standard position passes through the point.

`tan theta = (-1/2)/(-sqrt 3/2)`

=> `tan theta = 1/(sqrt 3)`

=> `theta = tan^-1(1/sqrt 3)`

=> `theta = 120 degrees`

**The measure of angle `theta` is 120 degrees.**