特征方程 4r^2 +4r +1=0, r1=r2=-1/2基本解组: e^(-x/2 ), x*e^(-x/2 )这就是两个线性无关解。通解 y=c1*e^(-x/2 )+c2*x*e^(-x/2 )=(c1+c2*x)e^(-x/2 )y'=c2*e^(-x/2 )-(1/2)(c1+c2*x)e^(-x/2 )=(1/2)(2c2-c1-c2*x)e^(-x/2 )y((0)=2,y'(0)=0得 c1=2,c2=1特解y=(1+2x)e^(-x/2 )