分类：教育/科学-学习帮助
问题：初二几何求助 
回答：过P,Q作BC平行线与AM分别交于D,E

AB/AP=AM/AD
AC/AQ=AM/AE
==>AB/AP+AC/AQ=AM(1/AD+1/AE)

PD/BM=AD/AM
EQ/CM=AE/AM
==>PD/EQ=AD/AE
PD/EQ=DN/EN
==>AD/AE=DN/EN
==>DN/AD=EN/AE
==>1+DN/AD+1-EN/AE=2
==>(AD+DN)/AD+(AE-EN)/AE=2
==>AN/AD+AN/AE=2
==>1/AD+1/AE=2/AN

==>AB/AP+AC/AQ=2AM/AN