如圖1，線段AC＝6cm，線段BC＝15cm，點M是AC的中點，在CB上取一點N，使得CN：NB＝1：2，求M...

問題詳情：

如圖1，線段AC＝6cm，線段BC＝15cm，點M是AC的中點，在CB上取一點N，使得CN：NB＝1：2，求MN的長．

【回答】

解：∵M是AC的中點，AC＝6，

∴MC＝AC＝6×＝3，·············································································· 1分

又因為CN∶NB＝1∶2，BC＝15，

∴CN＝15×＝5，·························································································· 3分

∴MN＝MC＋CN＝3＋5＝8，

∴MN的長為8 cm·························································································· 4分 

知識點：直*、*線、線段

題型：解答題