cos=ab/|a||b|=根号3/2
得ab=3/2
(a+b)(a-b)=|a|^2-|b|^2=2
|a+b|=根号[(a+b)^2]=根号7
|a-b|=根号[(a-b)^2]=1
cos=(a+b)(a-b)/|a+b||a-b|=2/根号7