Find if , , , , and angle between and is .
I've tried to substitute and by doing a cross product leading me to the expression .
My book gives this solution: .
Again, this is my approach to this problem:
so... I stopped here because I didn't know what to do.
So, here I need your help on this. I appreciate the alexmahone's help, but I'm looking to solve the problem using the facts that were mentioned in problem.