Question

已知向量A=(cosa,sina) ,向量B=(cosb,sinb)

Answer 1

1

(A+B)*(A-B)

=(cosa+cosb)(cosa-cosb)+(sina+sinb)(sina-sinb)

=1-1=0

(A+B)垂直（A-B)

2

A×B=|A||B|sin=3/5

|A|=|B|=1

sin=3/5

cos=4/5 或 cos=-4/5

A*B=cosacosb+sinasinb=cos(a-b)=|A||B|cos

cos(a-b)=4/5

-π/2