Determine whether the angle between u=[2, 1] and v=[1, -3] is acute, obtuse, or a right angle.
The Attempt at a Solution
a*b=2*1+1(-3)=2+(-3)=-1, since the answer is negative, it means the angle is obtuse, am I right? Or is this even the right way of doing this problem? If not, then please correct me.