To find the measure of arc AB when the measure of angle APB is 78 degrees, we can use the fact that the measure of an inscribed angle is half the measure of the arc it intercepts. In this case, angle APB intercepts arc AB.
Therefore, if m∠APB = 78°, the measure of arc AB is given by:
Measure of arc AB = 2 × m∠APB
Substituting the given value:
Measure of arc AB = 2 × 78° = 156°.
So, the measure of arc AB is 156 degrees.