The sine value of 120 degrees is equal to 0.866, rounded to the third decimal. This value is equal to the square root of 3 divided by 2.
Values for trigonometric functions at specific angles are found through the unit circle. This mathematical device equates the values of sine and cosine, the other basic trigonometric functions, to specific important angles. Regardless of the position on the unit circle, the value of both basic functions always lies between negative 1 and positive 1. The unit circle also works in radians, which is a common mode on many calculators. In radians, 120 degrees is equal to 2(pie)/3, where pie is approximately 3.14.