第三种方法是把待求级数用基本初等函数的幂级数展开式表示出来；

The third one is to let series be expressed by basic elementary function's power series expansion;

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第三种方法是把待求级数用基本初等函数的幂级数展开式表示出来；

The third one is to let series be expressed by basic elementary function's power series expansion;

youdao