Sine of angle

A corner is a geometric figure formed by two rays (sides of an angle) coming from one point (which is called the vertex of the angle). A plane containing both sides of an angle is divided by an angle into two areas. Each of these areas, combined with the sides of the corner, is called a flat angle (or simply an angle, if this does not cause discrepancies). One of the flat corners (usually the smaller of the two) is sometimes conventionally called internal, and the other external. Points of a flat angle that do not belong to its sides form the inner region of the flat angle.

Initially, the definitions of trigonometric functions, the argument of which is an angle, were expressed in terms of the aspect ratios of a right triangle. The sine of the angle (sin α) is the ratio of the opposite side of the leg to the hypotenuse.