Question

giúp mình với 

x³-7x-6=0

Answer 1

`x^3-7x-6=0`

`<=>x^3+x^2-x^2-x-6x-6=0`

`<=>x^2(x+1)-x(x+1)-6(x+1)=0`

`<=>(x+1)(x^2-x-6)=0`

`<=>(x+1)(x^2-3x+2x-6)=0`

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

`<=>` $\left[\begin{matrix} x=-1\\ x=3\\x=-2\end{matrix}\right.$

Vậy `S={-1;-2;3}`

Answer 2

x³ - 7x - 6 = 0 

<=> x³ - x - 6x - 6 = 0

<=> x(x - 1) ( x + 1) - 6 ( x + 1) = 0

<=> (x + 1) ( x² - x - 6) = 0

<=> (x + 1) ( x- 3 ( x + 2) = 0

vậy x = [- 1 ; 3 ; - 2]

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