Question

what is the measure of angle coa?
140°
150°
160°
170°

Explanation:

Step1: Recall inscribed angle theorem

An inscribed angle is half the measure of its intercepted central angle. $\angle ABC$ is an inscribed angle intercepting arc $AC$, and $\angle COA$ is the central angle intercepting the same arc.

Step2: Calculate central angle

Multiply inscribed angle by 2.
$\angle COA = 2 \times \angle ABC = 2 \times 80^\circ$

Answer:

160°