六年制重点中学高中《代数》第二册中,我们已经接触了重要的不等式|a±b|≤|a|+|b|(a,b∈R)。但是,课本中没有指出不等式取等号的条件,因此学生往往忽视了这个问题的作用。本文把上述不等式作一些补充,并举数例说明其用途。定理1 不等式|a+b|≤|a|+|b|当且 In the second grade of the six-year key middle school high school algebra, we have already touched on the important inequality |a±b|≤|a|+|b|(a,b∈R). However, the textbook does not indicate the condition of the inequality for the equal sign, so students often overlook the role of this problem. This article makes some additions to the above inequality and gives a few examples of its use. Theorem 1 Inequality |a+b|≤|a|+|b|