首页 > 数学 > 题目详情
三角形ABC,已知角A是锐角,在AB上取一点D,AC上取一点E,连接CD,BE,使角DCB=角EBC=1/2角A,求BD与CE数量关
题目内容:
三角形ABC,已知角A是锐角,在AB上取一点D,AC上取一点E,连接CD,BE,使角DCB=角EBC=1/2角A,求BD与CE数量关优质解答
在CD上或CD的延长线上取一点F,使得:CF = BE .
在△CBF和△BCE中,CF = BD ,∠BCF = ∠CBE ,BC为公共边,
所以,△CBF ≌ △BCE ,可得:BF = CE ,∠CBF = ∠BCE ,∠CFB = ∠BEC .
① 若点F在CD上,则有:
∠BFD = ∠CBF+∠DCB = ∠BCE+∠DCB = ∠ACD+2∠DCB = ∠ACD+∠A = ∠BDF ;
可得:BD = BF = CE ;
② 若点F在CD的延长线上,则有:
∠BFD = ∠BEC = ∠ABE+∠A = ∠ABE+∠EBC+∠DCB = ∠ABC+∠DCB = ∠ADC = ∠BDF ;
可得:BD = BF = CE ;
③ 若点F和点D重合,
可得:BD = BF = CE ;
综上可得:BD = CE .
优质解答
在△CBF和△BCE中,CF = BD ,∠BCF = ∠CBE ,BC为公共边,
所以,△CBF ≌ △BCE ,可得:BF = CE ,∠CBF = ∠BCE ,∠CFB = ∠BEC .
① 若点F在CD上,则有:
∠BFD = ∠CBF+∠DCB = ∠BCE+∠DCB = ∠ACD+2∠DCB = ∠ACD+∠A = ∠BDF ;
可得:BD = BF = CE ;
② 若点F在CD的延长线上,则有:
∠BFD = ∠BEC = ∠ABE+∠A = ∠ABE+∠EBC+∠DCB = ∠ABC+∠DCB = ∠ADC = ∠BDF ;
可得:BD = BF = CE ;
③ 若点F和点D重合,
可得:BD = BF = CE ;
综上可得:BD = CE .
本题链接: