## Elementary Geometry for College Students (6th Edition)

The acute interiors angles of a regular pentagram measure 36$^{\circ}$.
Exterior angles of a pentagon. E=$\frac{360}{5}$ E=72$^{\circ}$ The acute angles of a pentagram are the third angle of isosceles triangles whose base angles are equal to the external angles of the pentagon. E+E+m$\angle$A=180 72+72+m$\angle$A=180 m$\angle$A=36