换元法在解题中有着十分广泛的应用．在解分式方程和无理方程时，应用换元法能将无理方程转化为有理方程；将分式方程转化为整式方程；将高次方程转化为低次方程．变复杂为简单，从而使解法简捷．由于换元法在解分式方程和无理方程中起着十分重要的作用，因此在中考试题中经常 Replacement method has a very wide range of applications in problem solving. In solving fractional equations and irrational equations, the application of the substitution method can transform irrational equations into rational equations; convert fractional equations into integral equations; convert higher-order equations into lower-order equations. Complexity is simple, so that the solution is simple. Since the substitution method plays a very important role in solving fractional equations and irrational equations, it is often used in examination questions.