死算出來的。一直沒想出純幾何方法求h

來源: 2011-08-15 14:39:14 [舊帖] [給我悄悄話] 本文已被閱讀:

h = hight of the arc. and A = 2*Pi*R*h

L = tangent line. 2a = chord.

L^2 = r*(2R + r), a^2 = h*(2R - h), and substitue them in

(h + r)^2 = L^2 - a^2

h = Rr/(2(R+r)).