The following are all vectors:
a, b, c, d
k = (a+b) (c+d)
prove: k = (a x c) + (a x d) + (b x c) + (b x d)
The Attempt at a Solution
I have tried to start it by doing:
|a| = a = sqrt(a_x^2 + a_y^2)
is that a correct start at it? I really am pretty lost...