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.
When you generalize the radius to any length, the lengths change in proportion resulting in the trigonometric ratios. The radius is referred to as the hypotenuse. These proportions form the primary trigonometric ratios.
Keep in mind the right angle triangle can be oriented in different ways. However, the sides are still in relation to the angle.