代数式的求值问题有两类:一类是给出字母的取值,直接带入求值;还有一类则是给定一个条件等式,而式中的字母又无法具体求解或者求起来不便,这时就可以考虑用整体的思想代入求值.一、直接进行整体代入1.当(a-b)/(2a+b)=5时,求3(a-b)/(2a+b)+(2a+b)/2(a-b)的值.解∵(a-b)/(2a+b)=5, There are two types of algebraic evaluation problems: one is to give the value of the alphabet, directly into the evaluation; there is a class is given a conditional equation, and formula in the letter and can not solve or find it inconvenient , Then you can consider the whole idea of ​​substitution into the value of 1. First, the direct substitution into the whole 1. (ab) / (2a + b) = 5, seeking 3 (ab) / (2a + b) + b) / 2 (ab). Solution (ab) / (2a + b) = 5,