Question

设e1,e2是两个不共线的向量,已知向量AB=2e1 ke2,向量CB=e1 3e2,向量CD=2e1-e2,若

Answer 1

可设AB=(2,k)CB=(1,3)CD=(2,-1)

BD=BC+CD=CD-CB=(1,-4)

A,B,D三点共线,AB//BD

(2,k)=j(1,-4)

2=j,k=-4j

k=-8