(1/ha)² + (1/hb)² + (1/hc)² = 1/R²
The a, b, c attached to h’s should be subscripts. In the regular heptagon and the heptagonal triangle, a = side length, b = length of short diagonal, c = length of long diagonal, R = length of circumradius, ha = altitude off side a, hb = altitude of side b, hc = altitude of side c & Δ = area of