Giải thích các bước giải:
c) `x^3-8x^2+21x-18=0`
`<=>(x^3-2x^2)-(6x^2-12x)+(9x-18)=0`
`<=>(x-2)(x^2-6x+9)=0`
`<=>(x-2)(x-3)^2=0`
`=>`\(\left[ \begin{array}{l}x=2\\x=3\end{array} \right.\)
Vậy `S={2;3}.`
d) `4/(x-1)-5/(x-2)=-3` $(ĐK:x \neq 1;2)$
`<=>(4(x-2)-5(x-1))/((x-1)(x-2))=-3`
`<=>4x-8-5x+5=-3(x-1)(x-2)`
`<=>x+3=3(x^2-3x+2)`
`<=>3x^2-9x+6-x-3=0`
`<=>3x^2-10x+3=0`
`<=>(3x^2-9x)-(x-3)=0`
`<=>(x-3)(3x-1)=0`
`=>`\(\left[ \begin{array}{l}x=3\\x=\dfrac13\end{array} \right.\) `(T//m text( ĐK))`
Vậy `S={3;1/3}.`
