x + y = 6(x + y)² = 36xy = 12x(6-x) = 12x² - 6x + 12 = 0x² - 6x + 9 = - 3(x - 3)² = - 3实数范围内无解。————————————————在复数范围的解是：x - 3 = ± √3 ix1 = 3 + √3 ix2 = 3 - √3 iy1 = 3 - √3 iy2 = 3 + √3 i
