Phần tích đã thức thành nhân tử xy(x+y) +yz(y+z) +xz(x+z) +2xyz

$xy(x+y)$ + $yz(y+z)$ + $xz(x+z)$ + $2xyz$

= xy(x + y) + yz(y + z) + xyz + xz(x + z) + xyz

= xy(x + y) + yz(y + z) + yz.x + xz(x + z) + xz.y

= xy(x + y) + yz(y + z + x) + xz(x + z + y)
= xy(x + y) + z(x + y + z)(y + x)
= (x + y)(xy + zx + zy + z²)
= (x + y)[x(y + z) + z(y + z)]
= (x + y)(y + z)(z + x)