如图, AM=1/3AB, AN=1/3AC.求证:MN=1/3BC.

问题描述:

如图 

AM
=
1
3
AB
 
AN
=
1
3
AC
.求证:
MN
=
1
3
BC

证明:∵

AM
=
1
3
AB
 
AN
=
1
3
AC

MN
=
AN
-
AM
=
1
3
(
AC
-
AB
)=
1
3
BC