三个“二次”是指二次函数、一元二次方程和二次不等式,三者之间存在紧密的联系。我们都知道,如果变量x,y之间满足y=ax2+bx+c(a、b、c为常数,且a≠0),则称y是x的二次函数。由于任何一个一元二次方程都可以化为ax2+bx+c=0的形式,所以,从“数”的角度来看,解一元二次方程ax2+bx+c=0就是求当二次函数y=ax2+bx+c的值等于0时,自变量相应的取值; Three “second ” refers to the quadratic function, quadratic equation and quadratic inequality, there is a close relationship between the three. We all know that y is a quadratic function of x if y = ax2 + bx + c (where a, b, c are constants, and a ≠ 0) between variables x and y. Since any one of the quadratic equations can be transformed into the form of ax2 + bx + c = 0, the solution of the quadratic equation ax2 + bx + c = 0 from the point of “number” When the value of the sub-function y = ax2 + bx + c is equal to 0, the corresponding value of the independent variable;