Y' = ( (x³)'*(2x + 4) - x³*(2x + 4)') / (2x + 4)² = (3x²*(2x + 4) - x³*2) / (2x + 4)² = (6x³ + 12x² - 2x³) / (2x + 4)² = (4x³ + 12x²) / (2x + 4)² = 4*(x³ + 3x²) / 4*(x + 2)² = (x³ + 3x²) / (x + 2)²