The y-coordinate of the point on the unit circle determined by a central angle (in standard position) of x radians is Sin(x). In a unit circle, the radian measure of an angle is the length of the arc subtended by that angle. To the left of the y-axis, you see a unit circle being swept out, with the radian measure of the angle (arc length) shown in blue, and the sine of that angle (the y-coordinate) shown in red. To the right of the y-axis, you see the points of the graph of y = Sin(x) being graphed in black. The angle x is shown in blue and the value of Sin(x) is shown in red.
Last modified, January 29, 2008