Muốn trừ hai phân số có cùng mẫu số thì:

\(\dfrac{9}{4}\)          

\(\dfrac{4}{9}\) 

\(\dfrac{{ - 4}}{9}\)

Tất cả các đáp án trên đều đúng

\(\dfrac{3}{7};\dfrac{7}{3}\) 

\(\dfrac{{11}}{{15}};\dfrac{{ - 11}}{{15}}\)  

\(5; - \dfrac{1}{5}\)

\(\dfrac{8}{9};\dfrac{9}{8}\)

\(\dfrac{{-14}}{{56}}\) 

\(\dfrac{{ - 15}}{{56}}\)  

\(\dfrac{-21}{{56}}\)

\(\dfrac{{ 15}}{{56}}\)

\(\dfrac{{27}}{{17}}\)  

\(\dfrac{{45}}{{17}}\)           

\(\dfrac{{24}}{{27}}\)

\(  \dfrac{{-45}}{{17}}\)

\(\dfrac{{ - 2}}{{15}}\)

\(\dfrac{{ - 2}}{{25}}\)  

\(\dfrac{{ - 3}}{{15}}\)

\(\dfrac{3}{{25}}\)

\( - \dfrac{1}{{15}}\) 

\(\dfrac{1}{6}\)  

\(\dfrac{1}{{15}}\)

\(\dfrac{1}{{10}}\)

\(\dfrac{4}{{21}}\) 

\(\dfrac{{ - 1}}{{42}}\)  

\(\dfrac{1}{6}\)

\( - \dfrac{4}{{21}}\)