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.

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。

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Female desirability begins to be constructed in terms of irrational fashion and the high heel - once separated from its original function of horseback riding - becomes a primary example of impractical dress.

BBC: Why did men stop wearing high heels?

The global economy is a complex system and is a function of millions of individual actors making decisions for both rational and irrational reasons.

FORBES: The Bailout Mentality -- The REAL "New Normal"