Values of the sine function on a unit circle
Here is a bit of history. A long time ago, all six trig functions were defined by the lengths of the sides of a triangle, the chord, and the secant as part of the unit circle. The secant line is not included in this applet, but the line segment OC is defined as the sine of the angle OCA. You will see that the sine of the angle is half of the chord of the unit circle. The Father of Trigonometry Hipparchus (120 B.C.E) created a table of chords which will later be known as the sine vaules of the trigonometric table.
Trigonometric table for sine:
sin(0)=0, sin(30)=1/2, sin(45)=2^(1/2)/2, sin(60)=3^(1/2)/2, sin(90)=1