Rút gọn phân thức : x^4 - y^4 / y^3 - x^3

* Hướng dẫn giải

$\frac{{\mathrm{x}}^4-{\mathrm{y}}^4}{{\mathrm{y}}^3-{\mathrm{x}}^3}=\frac{\left({\mathrm{x}}^2-{\mathrm{y}}^2\right)\left({\mathrm{x}}^2+{\mathrm{y}}^2\right)}{-\left(\mathrm{x}-\mathrm{y}\right)\left({\mathrm{x}}^2+\mathrm{xy}+{\mathrm{y}}^2\right)}=\frac{\left(\mathrm{x}+\mathrm{y}\right)\left({\mathrm{x}}^2+{\mathrm{y}}^2\right)}{-{\mathrm{x}}^2-\mathrm{xy}-{\mathrm{y}}^2}$