E= { x thuộc R l ( x^2 – 10x + 21 ) ( x^3 – x ) = 0

`(x^2 – 10x + 21)(x^3 – x) = 0`

`<=>(x^2-3x-7x+21)(x^2-1)=0`

`<=>x(x-7)(x-3)(x^2-1)=0`

`<=>(x(x-7)(x-3)(x-1)(x+1)=0`

`⇔` \(\left[ \begin{array}{l}x=0\\x-7=0\\x-3=0\\x-1=0\\x+1=0\end{array} \right.\)

`⇔` \(\left[ \begin{array}{l}x=0\\x=7\\x=3\\x=1\\x=-1\end{array} \right.\)

`⇔ E = {0;7;3;1;-1}`

Xin hay nhất !