joelkoerwer at gmail.com
Sun Aug 26 21:23:09 EDT 2007
x is called the sagitta. At least when making a telescope mirror it is.
By bisecting your angle with another radius, you'll see that you have
a right triangle with hypotenuse a, and legs of length (b/2) and
sagitta a b = a - sqrt (a*a - b*b/4)
Considered as a function of half the angle subtended by the points on
the circumference, this is called the versine.
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