特征方程是r^4+2r^3+2r^2=0即r^2(r^2+2r+2)=0解得r1=r2=0,r3,4=-1±ir1=r2=0对应C1 x+C2r3,4=-1±i对应e^(-x) * (C3 cosx+C4 sinx)所以通解是y=C1 x+C2+e^(-x) * (C3 cosx+C4 sinx)
