A figure formed by two rays which start from a common point (a plane angle) or by three planes that intersect (a solid angle).
the angle between lines A and B
The measure of such a figure. In the case of a plane angle, this is the ratio (or proportional to the ratio) of the arc length to the radius of a section of a circle cut by the two rays, centered at their common point. In the case of a solid angle, this is the ratio of the surface area to the square of the radius of the section of a sphere.
The angle between lines A and B is π/4 radians, or 45 degrees.