The Sine Graph in Radians

Most graphs of trig functions label the angle axis in radians: 90° is π/2, 180° is π, 270° is 3π/2 and a full turn, 360°, is 2π. The wave is the same; only the labels change.

On a radian axis the sine graph rises from 0 to its top, 1, at π/2, is back to 0 at π, falls to −1 at 3π/2 and is at 0 again at 2π. Its period is 2π, so the top comes again at π/2 + 2π = 5π/2, and a lap earlier at π/2 − 2π = −3π/2.

To write an angle in radians, divide its degrees by 180 and multiply by π. 30° is π/6, so the two heights of 1/2 in the first lap, at 30° and 150°, sit at π/6 and 5π/6.