Answer:
180° - (360/n)°, where n is the number of sides of the polygon.
Explanation:
Polygon has n sides.
Divide the polygon radially into n congruent, isosceles triangles.
For each triangle:
vertex angle = (360/n)°
sum of base angles = 180° - vertex angle = 180° - (360/n)°
Each interior angle of the n-gon = 180° - (360/n)°