看图片
y'' - y' = x特征方程 r^2-r = 0, r = 0, 1设特解 y = x(ax+b) = ax^2+bx则 2a - 2ax - b = x， a = -1/2, b = -1特解 y = -(1/2)x^2 - x通解 y = C1 + C2e^x - (1/2)x^2 - x
