Giải:
a) \(\dfrac{1}{3}\left(xy\right)^3.\left(-2\right)x.\dfrac{-3}{5}y^5z\)
\(=\dfrac{1}{3}.\left(-2\right).\dfrac{-3}{5}x^3y^3xy^5z\)
\(=\dfrac{2}{5}x^4y^8z\)
Vậy ...
b) \(-\dfrac{1}{3}x^2yz.\dfrac{1}{7}\left(xy\right)^4.\dfrac{7}{9}xyz^3\)
\(=-\dfrac{1}{3}.\dfrac{1}{7}.\dfrac{7}{9}x^2yz.x^4y^4.xyz^3\)
\(=-\dfrac{1}{27}x^7y^6z^4\)
Vậy ...