Unit 3 Damped Oscillations (18.03x Differential Equations, course 1-Introduction to Differential Equations) 更新截止到高阶ODE，暂停课程。

整理了小诗集，制作成pdf了

Unit 2 Complex Exponentials and ODEs (18.03x Differential Equations, course 1-Introduction to Differential Equations)

Unit 1 Modeling and First Order ODEs (18.03x Differential Equations, course 1-Introduction to Differential Equations)