The Yff contact circle is the circumcircle of the Yff contact triangle. Its center has triangle center function α = ((b - c)(3a^3 + b^3 + c^3 - 2a^2 b - 2a^2 c - a b c))/a, which does not correspond to any Kimberling center. Its radius is R_Y = 1/(2 left bracketing bar (a - b)(b - c)(c - a) right bracketing bar ) sqrt((f(a, b, c) f(b, c, a) f(c, a, b))/(a + b + c)), where f(a, b, c) = a^3 - 2c a^2 + b c a + b^3 + c^3 - 2b^2 c.

central circle | Yff contact triangle