An angle that has a magnitude, as well as the direction of rotation, is known as the directed angle. An angle in the figure is formed by two rays called the initial ray and terminal ray, with a common initial point called a vertex.
If the rotation from the initial ray to the terminal ray is clockwise it is to be taken as positive and if it is anti-clockwise, rotation is to be taken as negative. Each trigonometrical ratio is a real number and has no units.