4、原式=x² + 3x + (3/2)² - (3/2)² - 1=(x + 3/2)² - 13/4∴最小值是-13/45、原式=-2(x² - 5x/2) + 3=-2[x² - 5x/2 + (5/4)² - (5/4)²]+3=-2(x - 5/4)² + 49/8∴最大值是49/8
画图就能求解
