向量a+b与2a-b垂直,a-2b与2a+b也垂直.则
(a+b)*(2a-b)=0
则2a^2+ab-2b^2=0
(a-2b)*(2a+b)=0
则2a^2-3ab-4b^2=0
联立解得
a^2=-5/2ab b^2=-2ab
则a与b的夹角的余弦值
cosa=ab/|a||b|
=ab/根号(-5/2ab*-2ab)
=1/根号5
向量a+b与2a-b垂直,a-2b与2a+b也垂直.则
(a+b)*(2a-b)=0
则2a^2+ab-2b^2=0
(a-2b)*(2a+b)=0
则2a^2-3ab-4b^2=0
联立解得
a^2=-5/2ab b^2=-2ab
则a与b的夹角的余弦值
cosa=ab/|a||b|
=ab/根号(-5/2ab*-2ab)
=1/根号5