已知二次函数y=ax~2+bx+c(a≠0),设自变量的取值范围是x_1≤x≤x_2,其最值可分为以下几种情况讨论求得:(1)若a>0,给定区间(自变量的取值范围)在对称轴x=-(b/2a)的左侧时(图1),函数的最大值和最小者分别为函数在x=x_1和x=_2时的函数值;(2)若a>0,给定区间横跨对称轴x=-(b/2a)时(图2),函数的最大值为函数在x=x_1和x=x_2时较大的值,最小值为当x=-(b/2a)时, It is known that the quadratic function y = ax ~ 2 + bx + c (a ≠ 0), and the range of independent variables is x_1≤x≤x_2. The maximum value can be divided into the following cases: ) If a> 0, given the interval (argument range) on the left side of the axis of symmetry x = - (b / 2a) (Figure 1), the maximum and minimum functions are the functions at x = x1 and x = _2; (2) If a> 0, the maximum value of the function for a given interval spanning the axis of symmetry x = - (b / 2a) x = larger value of x_2, the minimum value is when x = - (b / 2a)