1. The problem asks to find the endpoint of the radius of the unit circle corresponding to 120 degrees. 2. Recall that the unit circle has radius 1, and the coordinates of a point on the unit circle at an angle $\theta$ are given by $(\cos \theta, \sin \theta)$. 3. Since $120^\circ = 90^\circ + 30^\circ$, the point lies in the second quadrant where $x$ is negative and $y$ is positive. 4. Using the special angles, $\cos 120^\circ = -\frac{1}{2}$ and $\sin 120^\circ = \frac{\sqrt{3}}{2}$. 5. Therefore, the endpoint of the radius at 120 degrees on the unit circle is $$\left(-\frac{1}{2}, \frac{\sqrt{3}}{2}\right).$$