Question #e0335

1 Answer
Mar 30, 2015

This is because if the set #A# is empty, you can't put at the first position anything...

You can also see this, remembering that the cross product can be imagined like a rectangle in which in one side there are the elements of #A# and in the other side there are the elements of #B#.
The possible couples you can do are the area of that rectangle.
But if one side has lenght zero... the area is zero!