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- Hướng dẫn giải

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

= $x^2$y + x$y^2$ + yz(y + z) + $x^2$z + x$z^2$ + xyz + xyz

= ($x^2$y + $x^2$z) + yz(y + z) + (x$y^2$ + xyz) + (x$z^2$ + xyz)

= $x^2$(y + z) + yz(y + z) + xy(y+ z) + xz(y + z)

= (y + z)( $x^2$ + yz + xy + xz) = (y + z)[($x^2$ + xy) + (xz + yz)]

= (y + z)[x(x + y) + z(x + y)] = (y + z)(x+ y)(x + z)