Suppose and intersect at point .
If two chords intersect at a point inside a circle, then the
measure of the included angle equals half the sum of the measures
of the two opposite arcs. First, use this fact to solve for the
measure of arc as follows:
The measure of an inscribed angle is half the measure of the arc
that subtends it. This means that the measure of is half the
measure of arc . Now use this fact to solve for the measure of .