Rút gọn phân thức: x^4 - 5x^2 +4 / x^4 -10x^2 + 9

* Hướng dẫn giải

$\begin{array}{l}\frac{{\mathrm{x}}^4-5{\mathrm{x}}^2+4}{{\mathrm{x}}^4-10{\mathrm{x}}^2+9}=\frac{{\mathrm{x}}^4-4{\mathrm{x}}^2-{\mathrm{x}}^2+4}{{\mathrm{x}}^4-9{\mathrm{x}}^2-{\mathrm{x}}^2+9}\\ =\frac{{\mathrm{x}}^2\left({\mathrm{x}}^2-4\right)-\left({\mathrm{x}}^2-4\right)}{{\mathrm{x}}^2\left({\mathrm{x}}^2-9\right)-\left({\mathrm{x}}^2-9\right)}=\frac{\left({\mathrm{x}}^2-4\right)\left({\mathrm{x}}^2-1\right)}{\left({\mathrm{x}}^2-9\right)\left({\mathrm{x}}^2-1\right)}=\frac{{\mathrm{x}}^2-4}{{\mathrm{x}}^2-9}\end{array}$