ac^2 - ad - bc^2 + cd + bd - c^3 = c^2(a - b) - d(a - b) + cd - c^3 = (c^2 - d)(a - b) + cd - c^3 = (c - d)(c + d)(a - b) + c(d - c^2) = (c - d)(c + d)(a - b - c)