1.二次函数的一般式y=ax~2+bx+c(c≠0)中有三个参数a,b,c.解题的关键在于:通过三个独立条件“确定”这三个参数.例1.已知f(x)=ax~2+bx,满足1≤f(-1)≤2且2≤f (1)≤4,求f(-2)的取值范围.分析:本题中,所给条件并不足以确定参数a,b的值,但应该注意到:所要求的结论不是f(-2)的确定值, 1. The general equation of quadratic function y=ax~2+bx+c(c≠0) has three parameters a, b, c. The key to solve the problem lies in: through three independent conditions “determined” these three Parameters. Example 1. Given that f(x) = ax~2+bx, satisfies 1≤f(-1)≤2 and 2≤f(1)≤4, find the value range of f(-2). Analysis: In this case, the conditions given are not sufficient to determine the values ​​of the parameters a, b, but it should be noted that the required conclusion is not a definite value of f(-2),