如图,已知AB//CD,∠B=120°,∠E=80°,求∠C的度数.

过E点向左做一条AB的平行线EF
则∠B+∠BEF = 180°
则∠BEF = 180°- ∠B = 60°
∠CEF = ∠E - ∠BEF = 80°- 60° = 20°
因为AB//CD AB//EF
则CD//EF
则∠C = ∠CEF = 20°