a)$\frac{14xy^5(2x-3y)}{21x²y(2x-3y)²}$ ĐKXĐ: x$\neq$ 0; y$\neq$ 0
= $\frac{2y^4}{3x(2x-3y)}$
= $\frac{2x^4}{6x²-9xy}$
b)$\frac{8xy(3x-1)³}{12x³(1-3x)}$ ĐKXĐ: x$\neq$ 0; x$\neq$ $\frac{1}{3}$
= -$\frac{8xy(3x-1)³}{12x³(3x-1)}$
= -$\frac{2y(3x-1)²}{3x²}$
= -$\frac{18x²y-12xy+2y}{3x²}$