特征方程 2r^2 + r -1 = 0 , (r+1)(2r-1) = 0, r = -1, 1/2故可设特解 y = ae^x, 代入微分方程得 a = 3/2则原微分方程通解是 x = C1e^(-x) + C2e^(x/2) + (3/2)e^x
