The perpendicular distance from an arc's midpoint to the chord across it, equal to the radius minus the apothem ,

(1)

For a regular polygon of side length ,

			(2)
			(3)
			(4)
			(5)
			(6)

where is the circumradius, the inradius, is the side length, and is the number of sides.

CITE THIS AS:

Weisstein, Eric W. "Sagitta." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/Sagitta.html