– I hear Tom is leaving. –____________ why?
A:And
B:But
C:Or
D:So
给定两个向量a→=(3,4),b→=(2,1),若(a→+xb→)⊥(a→﹣b→),则x的值等于____ .
已知|a|=3,b2=16,且|a+b|≠a+b,则代数式a﹣b的值为( )