In this section we’ll only consider sines of angles between 0° and 90°. In the section on trigonometric functions, we’ll define sines for arbitrary angles.

A sine (*CE*)* *is half of a chord (*CD*). More accurately, the sine of an angle (*CAB*) is half the chord of twice the angle (*CAD*). Inside the circle segment, a right angle triangle *ACE* is formed.

In a unit circle, where the radius is of length 1. Sine (or sin) represents the opposite side of angle *CAE*. Cosine (or cos) represents what is called the adjacent side *AE *to angle *CAE*.