令 y = 1-x, 则 x = 1-y则 f(x) = 1+x+x^2+x^3 = 1 + 1-y + (1-y)^2 + (1-y)^3= 5 - 6y + 4y^2 - y^3f(0.98) = 5 - 6*0.02 + 4*0.02^2 - ... ≈ 5 - 0.12 = 4.88
