Ta có :
\(\frac{9x-18}{18y-54}=\frac{9\left(x-2\right)}{9\left(2y-6\right)}=\frac{x-2}{2y-6}\) (1)
\(\frac{2x-4}{4y-12}=\frac{2\left(x-2\right)}{2\left(2y-6\right)}=\frac{x-2}{2y-6}\) (2)
Từ (1) ; (2) => \(\frac{9x-18}{18y-54}=\frac{2x-4}{4y-12}\) (đpcm)