Rút gọn rồi quy đồng mẫu: \(\dfrac{{120}}{{40}},\dfrac{{ - 280}}{{600}}\) và \(\dfrac{{ - 18}}{{75}}\)

* Hướng dẫn giải

\(\eqalign{  & {{120} \over {40}} = {{120:40} \over {40:40}} = {3 \over 1},  \cr  & {{ - 280} \over {600}} = {{ - 280:40} \over {600:40}} = {{ - 7} \over {15}},  \cr  & {{ - 18} \over { - 75}} = {{18} \over {75}} = {{18:3} \over {75:3}} = {6 \over {25}}. \cr} \)

Do đó: 

\(\eqalign{
& \frac{{120}}{{40}} = \frac{3}{1} = \frac{{3.75}}{{1.75}} = \frac{{225}}{{75}}; \cr
& \frac{{ - 280}}{{600}} = \frac{{ - 7}}{{15}} = \frac{{ - 7.5}}{{15.5}} = \frac{{ - 35}}{{75}}; \cr
& \frac{{ - 18}}{{ - 75}} = \frac{{18}}{{75}} = \frac{6}{{25}} = \frac{{6.3}}{{25.3}} = \frac{{18}}{{75}}. \cr} \)