见图
y = 3(x^2-2x+4)^(-1),
y' = -3(x^2-2x+4)^(-2) (2x-2) = -6 (x-1)(x^2-2x+4)^(-2)
y'' = -6[(x^2-2x+4)^(-2) - 2(x-1)(x^2-2x+4)^(-3) (2x-2)]
= -6[(x^2-2x+4)^(-2) - 4(x-1)^2(x^2-2x+4)^(-3)]
= -6 [(x^2-2x+4) - 4(x-1)^2] / (x^2-2x+4)^3
= 18x(x-2)/(x^2-2x+4)^3