In a triangle ABC, if AB = AC and angle B = 50^circ, then the measure of angle A is:

Since $AB = AC$, the angles opposite to them are equal, so $\angle C = \angle B = 50^\circ$. Using the angle sum property of a triangle, $\angle A + \angle B + \angle C = 180^\circ$, which gives $\angle A + 50^\circ + 50^\circ = 180^\circ$, resulting in $\angle A = 80^\circ$.