特征方程r^4+1=0,r^4=-1=cosπ+isinπ故r=cos(π/4+kπ/2)+isin(π/4+kπ/2), k=0,1,2,3=±1/√2±i/√2所以通解为; y=e^(x/√2)[C1cos(x/√2)+C2sin(x/√2)]+e^(-x/√2)[C3cos(x/√2)+C4sin(x/√2)]
