How to calculate the angle of a vector from the vertical?

Question

Im trying to find out the angle (in degrees) between two 2D vectors. I know I need to use trig but I\'m not too good with it. This is what I\'m trying to work out (the Y axi

Answer 1

The angle of the second vector relative to the first = atan2(y2,x2) - atan2(y1,x1).

http://www.euclideanspace.com/maths/algebra/vectors/angleBetween/index.htm