求多项式f(x)=x^3-6x^2+15x-14的所有有理根,并写出它在复数域,实数域和有理数域的标准分解式

f(x)=x^3-6x^2+15x-14
=x³-2x²-4x²+8x+7x-14
=x²(x-2)-4x(x-2)+7(x-2)
=(x-2)(x²-4x+7)
x²-4x+7=0 Δ=16-28=-12