对于不等式的证明 ,课本着重介绍了比较法、综合法、分析法 .其实 ,构造二次函数f(x) =ax2 +bx +c(a0 ) ,利用f(x) ≥ 0恒成立的充要条件Δ≤ 0和 f(x) 0恒成立的充要条件Δ0来证明 ,也是一种行之有效的方法 .下面以新教材第二册 (上 )课本中的几个习题为例加以说明 .一、若 For the proof of inequality, the textbook focuses on the comparison method, the synthesis method, and the analysis method. In fact, construct the quadratic function f(x) = ax2 + bx + c(a0) and use f(x) ≥ 0 to establish The condition Δ ≤ 0 and the necessary and sufficient condition for the constant f(x) 0 to be established are proved to be valid methods. Here is an example of a few exercises in the second volume of the new textbook (top). First, if