解答
The inscribed angle measures exactly half of the central angle (and half of the intercepted arc measure): $\theta_{\text{inscribed}} = \frac{1}{2} \theta_{\text{central}}$.
解説
Consequently, any inscribed angle that intercepts a diameter (a semicircle of $180^\circ$) is a right angle ($90^\circ$, Thales's Theorem).