来源:学生作业帮 编辑:搜搜考试网作业帮 分类:数学作业 时间:2024/06/30 08:56:42
如图,在三角形ABC中.题目如补充中所示.
![](http://img.wesiedu.com/upload/f/ea/fea251ca4d81e94ae2b8bc47c3fed4ae.jpg)
证明:
过点B作BE//AC,交AD延长线于E;连接BE.
M是BC中点 ==> BD=CD
BE//AC ==> ∠BED = ∠CAD
∠BDE =∠CDA
∴ ΔBDE ≌ ΔCDA ==> ED = AD;EB = AC;
ΔABE ==> AB + EB > AE
==> AB +AC > (AD+ED)
∵ ED = AD
∴ (AB +AC)/2 > AD