This article directly get it's special solution by the method of elementary integrals, and the method is simple and has wider range.

文章用初等积分法直接来求其特解，该方法简单、方便，且适用范围广。

youdao

What's a function, what's a derivative, what's a second derivative, how to take derivatives of elementary functions, how to do elementary integrals.

什么是函数,什么是导数,什么是二阶导数,如何对初等函数求导,如何进行初等积分

耶鲁公开课 - 基础物理课程节选