问题描述: 在三角形abc中,角acb=90度,d为bc中点,e为ad中点,fg平行ac,求证bf=2cg如图 1个回答 分类:数学 2014-09-29 问题解答: 我来补答 ∵∠CAD = 90°,E是AD的中点∴EC = ED = EA∴∠ECB = ∠GDC∵AC//GF∴EG:EA = FE:EC∴EG:EF = EC;EA∵∠CEG = ∠AEF∴△GEC∽△FEA∴∠GCE = ∠FAE∵∠CFB = ∠FAE +∠EAC+∠ACE∠CGD=∠EAC+∠ACE+∠ECG∴∠CFB = ∠CGD∴△CFB∽△DGC∴CB:CD = BF:GC ∵D是CB的中点∴CB:CD = 2:1∴BF:CG = 2:1∴2CG = BF 展开全文阅读