换元积分法（Integration By Substitution）是求积分的一种方法，主要通过引进中间变量作变量替换使原式简易，从而来求较复杂的不定积分。它是由链式法则和微积分基本定理推导而来的。
通过实例分析了在换元积分法中容易犯的一类错误及其产生的原因，指出了在解题中避免产生这类错误的一般方法。
Specific examples were cited to analyze the mistakes and causes in the use of integration by substitution, and the general method was pointed out to avoid such kinds of mistakes in operation.
第二换元积分法是求函数不定积分的一种重要方法，具有一定的适用范围，对某些无理函数的积分的求解通常使用该方法。
The integration by second substitution is an important method of calculating indefinite integral, it has a certain application, it usually applies to calculate some integrals of irrational function.
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