a*b=-2*(-3)=6
|a|=sqrt(9+4)=sqrt(13)|b|=2
cos<a,b>=a*b/(|a|*|b|) =6/(2sqrt(13))=3sqrt(13)/13
<a,b>=arccos 3sqrt(13)/13
a*b=-2*(-3)=6
|a|=sqrt(9+4)=sqrt(13)
|b|=2
cos<a,b>=a*b/(|a|*|b|) =6/(2sqrt(13))=3sqrt(13)/13
<a,b>=arccos 3sqrt(13)/13