(b-c) / b - c^2 / (b^2-bc) + 2b / (b-c) = (b-c) / b - c^2 / b(b-c) + 2b / (b-c) =
(b-c)*(b-c) / b - c^2 / b(b-c) + 2b*b/(b-c) = ((b-c)^2 - c^2 + 2b^2) / b(b-c) =
(b^2 - 2bc + c^2 - c^2 + 2b^2) / b(b-c) = (3b^2 - 2bc) / b(b-c) = b(3b-2c)/b(b-c) = (3b-2c)/(b-c)