The formula of 1 and two centroids is: RC = m1r1+M2R2+M3R3+.../∑ m.
2. centroid formula: xc = [∫ a (ρ xda)]/ρ a = [∫ a (xda)]/a = sy/a and YC = [∫ a (ρ yda)]/ρ a = [∫ a (yda)]