Question

如图，已知AB//CD，∠B=120°，∠E=80°，求∠C的度数。

全过程

Answer 1

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°

Answer 2

过点E做FE//AB
所以∠FBE=180-120=60
所以∠FEC=∠BEC-∠FBE=80-60=20
又AB//CD，所以FE//CD
所以∠C=∠FEC=20°

Answer 3

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°

Answer 4

20度!