Say we have to..
Find the angle (Theta) between the two vectors
U= cos(pi/4)i + sin(pi/4)j
V= cos(pi/2)i + sin(pi/2)j
When entering these 2 vectors using option 1 6 in Vector Calculus Made Easy we will not use the i-j notation and instead use vector /matrix notation as shown in this image . The angle is derived using arccos(AB/|A|*|B|) and given in radian format.
Note: We know that the vectors differ by an angle of pi/2-pi/4=pi/4 or .785 , which also equals 45 degrees.