a=π/4+kπ/2;k=0,1,2,3;
r=(+-)1/√2(+-)i/√2
通解就是=e^(x/√2)(C1cos(x/√2)+C2sin(x/√2))+e^(-x/√2)(C3cos(x/√2)+C4sin(x/√2))
特解=e^x