Rút gọn biểu thức: M = 4(x+3)/3x^2-x : x^2 +3x/ 1-3x

* Hướng dẫn giải

$\mathrm{M}=\frac{4\left(\mathrm{x}+3\right)}{3{\mathrm{x}}^2-\mathrm{x}}:\frac{{\mathrm{x}}^2+3\mathrm{x}}{1-3\mathrm{x}}=\frac{4\left(\mathrm{x}+3\right)}{\mathrm{x}\left(3\mathrm{x}-1\right)}.\frac{-\left(3\mathrm{x}-1\right)}{\mathrm{x}\left(\mathrm{x}+3\right)}=\frac{-4}{{\mathrm{x}}^2}$