一般地,我们把形如y=ax2+bx+c(其中a,b,c是常数,a≠0)的函数叫做二次函数,其中a称为二次项系数,b为一次项系数,c为常数项.x为自变量,y为因变量.等号右边自变量的最高次数是2.二次函数图像是轴对称图形.对称轴为直线x=-b/2a.对称轴与二次函数图像唯一的交点为二次函数图像的顶点P.特别地,当b=0时,二次函数图像的对称轴是y轴(即直线x=0).a,b同号,对称轴在y In general, we call quadratic functions of the form y = ax2 + bx + c (where a, b, c are constants, a ≠ 0), where a is called the quadratic coefficient and b is the coefficient of the first order. c is a constant term, x is an independent variable, y is a dependent variable, and the maximum number of independent variables to the right of the equal sign is 2. The quadratic function image is an axisymmetric graph whose axis of symmetry is a straight line x = -b / 2a. The only intersection of the sub-function images is the vertex P of the quadratic function image. In particular, the symmetry axis of the quadratic function image is the y-axis (ie, line x = 0) when b = In y