thank you that is very useful but i must be doing something wrong in my calculations the vector i get from those points are 3i+5j+0k for both, when i take the cross product the answer is 0. I know that is not correct. What's wrong with my calculations
Allie, a sketch always helps. What you're doing is... You're finding the vector of a diagonal of the parallelogram BC instead of the adjacent side, AC. Calculate the vector product .