换元法指的是将一个较复杂的代数式中的某部分看做一个整体,并用一个新的字母替代这个整体来运算,从而使运算过程简明清晰.换元法也是重要的一种数学方法,它的作用是可以化繁为简,化难为易,可以分散难点,换元法在整式运算、分式、分解因式中的运用较广,在解方程或方程组中更是不可缺少的方法. Reciprocation method refers to the part of a complex algebraic equation as a whole, and replaced by a new letter to calculate the whole, so that the calculation process is simple and clear.Replacement method is also an important mathematical method, Its role is to make it simple, easy and easy to disperse difficulties, for the yuan method in the whole operation, fractional factorization factor in the wider use of the equation or equations in the solution is an indispensable method .