sum of two reflections

The green dot is reflected in one of two intersecting lines. The image of the dot is then reflected in the other line. The sum of the two reflections is equivalent to a rotation about the point of intersection of the lines. What is the relationship between this angle of rotation and the angle between the intersecting lines? You can set the angle between the intersecting lines by dragging the orange dots. You can place the green dot wherever you like by dragging it.