a) $(5x^2y^3z).(-11xyz^4)$
$=5x^2y^3z.(-11)xyz^4$
$=(-11.5)(x^2x)(y^3y)(zz^4)$
$=-55x^3y^4z^5$
⇒ Hệ số: $-55$, bậc: $3+4+5=12$, biến: $x^3y^4z^5$
b) $(-6x^4y^4).(\dfrac{-2}{3}x^5y^3z^2)$
$=-6x^4y^4.\dfrac{-2}{3}x^5y^3z^2$
$=(-6.\dfrac{-2}{3})(x^4x^5)(y^4y^3)z^2$
$=4x^9y^7z^2$
⇒ Hệ số: $4$, bậc: $9+7+2=18$, biến: $x^9y^7z^2$