在二次函数学习和中考数学试题中,经常遇到让我们根据二次函数的图像判断a、b、c或某些代数式的值(或正负),由于某些式子比较难判断,很多同学在做这类问题时常常出错或不知从何入手,为了帮助大家解决这类问题,下面以近几年的中考题为例给出这类问题的常见解法,供大家参考. In the quadratic function test and the entrance examination math test, we often encounter the value of a, b, c or some algebraic values ​​(or positive and negative) that let us judge according to the quadratic function. Because some formulas are more difficult to judge, many Students often do something wrong or do not know where to start. In order to help you solve such problems, the following provides a common solution to these problems in the past few years for your reference.