what is the measure of a vertex angle
Vertex angle A vertex angle in a polygon is often measured on the interior side of the vertex. For any simple n-gon, the sum of the interior angles is π(n − 2) radians or 180(n − 2) degrees.[1]
Isosceles triangle In an isosceles triangle that has exactly two equal sides, the equal sides are called legs and the third side is called the base. The angle included by the legs is called the vertex angle and the angles that have the base as one of their sides are called the base angles.[6] The vertex opposite the base is called the apex.[7] In the equilateral triangle case, since all sides are equal, any side can be called the base.[8]