`x^3-7x-6`
$=x^3+x^2-x^2-x-6x-6$
$=\left(x^3+x^2\right)-\left(x^2+x\right)-\left(6x+6\right)$
$=x^2.\left(x+1\right)-x.\left(x+1\right)-6.\left(x+1\right)$
$=\left(x+1\right).\left(x^2-x-6\right)$
$=\left(x+1\right).\left(x^2+2x-3x-6\right)$
$=\left(x+1\right).\left[\left(x^2+2x\right)-\left(3x+6\right)\right]$
$=\left(x+1\right).\left[x.\left(x+2\right)-3.\left(x+2\right)\right]$
$=\left(x+1\right).\left(x+2\right).\left(x-3\right)$
Xin hay nhất !
