 This procedure produces the formula expressed using radian measure of angles.The part of the graph of sin("x") in the range from 0° to 180° "looks like" part of a parabola through the points (0, 0) and (180, 0).The general such parabola is

The parabola that also passes through (90, 1) (which is the point corresponding to the value sin(90°) = 1) is

The parabola which also passes through (30, 1/2) (which is the point corresponding to the value sin(30°) = 1/2) is

These expressions suggest a varying denominator which takes the value 90 × 90 when "x" = 90 and the value 2 × 30 × 150 when "x" = 30.