About mathf.sin()

Debug.Log("sin : " + Mathf.Sin(30));
why it give me sin : -0.988. As I know sin 30 = 1/2 or .5

All the Mathf trigonometric functions work in Radians, not Degrees.

Sin(30) = Sin(30 Radians) = Sin(1718.87 Degrees) = -0.988.