Example (1)y+2y=0:(ODE) 4日10y4至，1无2000 Peipei Shang School of Mathematical Sciences shang@tongji.edu.Ordinary Differential EquationsExample (1) y 0 +2xy = 0; (ODE) (2) xy 00 +y 0 = x 2 ; (ODE) (3) y 000 −x(y 0 ) 3 +y = 0; (ODE) (4) d 2 y dt 2 +y = cos 2t; (ODE) (5) ∂ 2T ∂ x 2 + ∂ 2T ∂ y 2 + ∂ 2T ∂ z 2 = 0; (PDE) (6) ∂ 2u ∂ x 2 = ∂u ∂ t +u. (PDE) Remark There are multiple criteria to classify ODEs. Peipei Shang School of Mathematical Sciences shang@tongji.edu.cn Ordinary Differential Equations