向量的基本概念 

1
5(3a-2b)-4(2b-3a)
=5(3a-2b)+4(3a-2b)
=9(3a-2b)
2
AE=2EC
即：EC=AC/3
BD=DC
即：CD=CB/2=(AB-AC)/2
故：ED=EC+CD
=AC/3+(AB-AC)/2
=AB/2-AC/6
=a/2-b/6
3
BD=BC+CD
=6e1+23e2+4e1-8e2
=10e1+15e2
=5(2e1+3e2)
=5AB
故：AB、BD共线
即：A、B、D共线