Question

己知AB=6㎝,c是线段AB延长线上点,M是线段AC的中点,N是Bc的中点求线段MN的长

Answer 1

解： 如图

设 BN=NC = x 

BM=y     则AM=6—y   

∵AM=MC

∴ 6—y=2x+y

2x+2y=6

2(x+y)=6

x+y=3

所以，MN=x+y=3

Answer 2

由题中已知条件可知：
AC=AB+BC
AM=1/2AC=1/2AB+1/2BC
AN=AB+1/2BC
于是可知：
MN
=AN-AM
=AB+1/2BC-(1/2AB+1/2BC)
=AB-1/2AB+1/2BC-1/2BC
=1/2AB
=1/2×6
=3