As shown in figure (1), it is known that AB is parallel to CD. What's the relationship between ∠ bed and ∠ B, ∠ D? Explain the reason and express it in words (geometric language)

As shown in figure (1), it is known that AB is parallel to CD. What's the relationship between ∠ bed and ∠ B, ∠ D? Explain the reason and express it in words (geometric language)

∠BED=∠B+∠D
Proof: make ef / / AB (F is on the right side of E)
∵EF//AB//CD
The two lines are parallel and the same angle is equal
∴∠BED=∠BEF+∠DEF=∠B+∠D

As shown in the figure, given ∠ B + ∠ d = ∠ bed, try to explain ab ‖ CD______ ∵∠BED=∠B+∠D，∴∠DEF=______ ．∴CD∥______ And ∵ ab ∥ EF, ∥ ab ∥______ ．

So the answer is: equal internal stagger angles, two parallel lines; ∵ bed = ∵ B + ∵ D, ∵ def = ∵ D, ∵ CD ∥ EF, ∥ ab ∥ CD