-(x² + 6x + 8) < x² - 2x + 5 < x² + 6x + 8 且x² + 6x + 8 > 0有 x² - 2x + 5 > -(x² + 6x + 8) ~ (1)x² - 2x + 5 < x² + 6x + 8 ~ (2)x² + 6x +...