Tính:

- Hướng dẫn giải

a) $27{\mathrm{x}}^6{\mathrm{y}}^{9 }+ 27{\mathrm{x}}^4{\mathrm{y}}^6{\mathrm{z}}^4 + 9{\mathrm{x}}^2{\mathrm{y}}^3{\mathrm{z}}^8 + {\mathrm{z}}^{12}$.

b) $\frac{{\mathrm{x}}^6}{{\mathrm{y}}^9}-\frac{3{\mathrm{x}}^4}{{\mathrm{y}}^3{\mathrm{z}}^2}+\frac{3{\mathrm{x}}^2{\mathrm{y}}^3}{{\mathrm{z}}^4}-\frac{{\mathrm{y}}^9}{{\mathrm{z}}^6}.$ 

c) $\frac{-8}{125}{\mathrm{a}}^6{\mathrm{b}}^6+\frac{12}{25}{\mathrm{a}}^4{\mathrm{b}}^6\mathrm{c}-\frac{6}{5}{\mathrm{a}}^2{\mathrm{b}}^6{\mathrm{c}}^2+{\mathrm{b}}^6{\mathrm{c}}^3.$ 

d) $\frac{8{\mathrm{c}}^3}{{\mathrm{d}}^6}+\frac{48\mathrm{c}}{{\mathrm{d}}^5}+\frac{96}{{\mathrm{cd}}^4}+\frac{64}{{\mathrm{c}}^3{\mathrm{d}}^3}.$