$\text{Đáp án + Giải thích các bước giải:}$
`x(x^{2}-4)=x^{2}-5x+6`
`<=>x(x-2)(x+2)=(x^{2}-2x)-(3x-6)`
`<=>x(x-2)(x+2)=x(x-2)-3(x-2)`
`<=>x(x-2)(x+2)=(x-2)(x-3)`
`<=>x(x-2)(x+2)-(x-2)(x-3)=0`
`<=>(x-2)[x(x+2)-(x-3)]=0`
`<=>(x-2)(x^{2}+2x-x+3)=0`
`<=>(x-2)(x^{2}+x+3)=0`
`<=>` \(\left[ \begin{array}{l}x-2=0\\x^{2}+x+3=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=2\\(x+\dfrac{1}{2})^{2}=-\dfrac{11}{4}\text{( Vô nghiệm )}\end{array} \right.\)
`\text{Vậy}` `S={2}`
