设特解为y2=Ax^2e^(3x)则y2'=(3Ax^2+2Ax)e^(3x)y2''=(9Ax^2+12Ax+2A)e^(3x)所以9Ax^2-18Ax^2+9Ax^2+12Ax-12Ax+2A=1所以A=1/2y2=x^2e^(3x)/2
