Given: ΔDFE is isosceles with base FE; FB ≅ EC. Prove: ΔDFB ≅ ΔDEC Triangle D F E is shown. 2 lines drawn down from point D to points C and B on the base of the triangle to form 3 triangles. Complete the missing parts of the paragraph proof. We know that triangle DFE is isosceles with base FE and that segment FB is congruent to segment EC because . Segment DF is congruent to segment by the definition of isosceles triangle. Since these segments are congruent, the base angles, angles , are congruent by the isosceles triangle theorem. Therefore, triangles are congruent by SAS.