如图,△ABC≌△DEC,∠ACB=80°,∠ACE=140°,求∠BCD的度数.

因为△ABC≌△DEC,∠ACB=80° ,所以,∠DCE=∠ACB=80°
因为 ∠ACE=140° , 所以 ∠BCE=∠ACE - ∠ACB = 140° - 80° = 60°

∠BCD = ∠DCE-∠BCE= 80° - 60° =20°