- #1

|XxY|=|X||Y|sin(<X,Y>) then

sin(<X,Y>)=|XxY|/(|X||Y|)

unfortunately i don't know when |XxY|>0 and when |XxY|<0 cause

|XxY|=(+/-)sqrt(sqr(XxY(1))+sqr(XxY(2))+sqr(XxY(3))).

how can i be sure when to use + when to use -?

or maybe there is another way to do it?