我们常常遇到这样的一类问题 :已知f(x)是关于 x的二次函数 ,其系数含有某给定区间 G上的单参数 t,且 t的最高次数为 1.求当 f(x)恒正 (负 )时 ,自变量 x的取值范围 .处理这类问题有一种简明而可靠的办法 :以参数 t为“主元”,将 f(x)转换成关于 t的“一次”函数 g(t) .然后利 We often encounter such a problem: we know that f(x) is a quadratic function about x, whose coefficients contain a single parameter t in a given interval G, and the highest number of times t is 1. Find f( x) Constant positive (negative), the range of values ​​of the independent variable x. There is a concise and reliable way to deal with this type of problem: convert the f(x) to t’s “once” with the parameter t as the “principal element”. The function g(t). Then