二次函数是中学数学的一个重点内容,既常作为中考压轴题,也是高中解二次不等式的重要方法,是数学中数形结合思想方法的体现。1认识二次函数(1)正方形的面积y与边长x之间的关系式y=x~2。(2)矩形周长为20,一边AB的长为x,矩形的面积y是x的函数,写出这个函数?解:y=-x~2+10x一般地,我们把形如y=ax~2+bx+c(a≠0)(a、b、c是常数且 The quadratic function is a key content of middle school mathematics, and it is often used as the final exam for senior high school students. It is also an important method for solving secondary inequalities in high school, and it is a reflection of the combination of number and shape in mathematics. 1 Recognize the quadratic function (1) The relation between the area y of the square and the length x of the square is y=x~2. (2) The perimeter of the rectangle is 20, the length of AB is x, and the area of ​​rectangle y is a function of x. Write this function? Solution: y=-x~2+10x Generally, we take the form of y=ax ~2+bx+c(a≠0) (a, b, c are constants and