Base Angles In An Isosceles Triangle Small 178×320 Medium 356×640 Large 570×1024 Download Tiff Original 1336×2400 | (192.5 KB) Description Illustration showing that can be used to prove that the base angles of an isosceles triangle are equal. Keywords base angles, congruent angles, equal, geometric proof, isosceles triangle, triangles, Vertex Galleries Geometric Theorems and Proofs Source: C. A. Hart & Daniel D. Feldman Plane And Solid Geometry (New York: American Book Company, 1911) 31