Determining the Angle Between Two Lines

In graphical applications, you often need to know the angle between two lines. You can move their intersection point to the origin easily, so all you need to do is choose a point on each line and find the angle between a line from the origin to that point and the x-axis. The angle between the lines is the difference. The arctangent of y/x is the mathematical function you need to find these angles, but VB