Question

如图,AB//CD,且∠1=∠2,∠3=∠4求证EF//MN

Answer 1

∵AB∥CD,∴∠2=∠3(两直线平行,内错角相等),

∵∠1=∠2,∠3=∠4,

∴∠1=∠2=∠3=∠4,

∵∠FEN=180°-(∠1+∠2),

∠MNE=180°-(∠3+∠4),

∴∠FEN=∠MNE,

∴EF∥MN(内错角相等,两直线平行).