特征方程：
r² + 2 = 0
r = ±√2i
y = C₁sin(√2x) + C₂cos(√2x)
令特解p = Asinx + Bcosx
p'' = - Asinx - Bcosx,代入方程得
(- Asinx - Bcosx) + 2(Asinx + Bcosx) = sinx
{ - A + 2A = 1 => A = 1
{ - B + 2B = 0 => B = 0
特p = sinx
∴方程通y = C₁sin(√2x) + C₂cos(√2x) + sinxr² + 2 = 0 r = ±√2i 是哪方面的知识？叫什么