Rút gọn biểu thức $A = \dfrac{{3.\left( { - 4} \right).60 - 60}}{{50.20}}$ ta được

$\dfrac{a}{b} = \dfrac{{a.m}}{{b.m}}\,$ 

$\dfrac{a}{b} = \dfrac{{a + m}}{{b + m}}\,$  

$\dfrac{a}{b} = \dfrac{{ - a}}{{ - b}}\,$            

$\dfrac{a}{b} = \dfrac{{a:n}}{{b:n }}$ với $n$ là ước chung của $a;b.$

$\left\{ {1; - 1} \right\}$         

$\left\{ 2 \right\}$  

$\left\{ {1;2} \right\}$

$\left\{ {1;2;3} \right\}$

$a = 3,b =  - 259$                

$a =  - 3,b =  - 259$  

$a = 3,b = 259$

$a =  - 3,b = 259$

$180$ 

$500$  

$750$ 

$450$

$\dfrac{{ - 2}}{4}$ 

$\dfrac{{ - 15}}{{ - 96}}$  

$\dfrac{{13}}{{27}}$

$\dfrac{{ - 29}}{{58}}$

$\dfrac{{16}}{{56}};\dfrac{{ - 35}}{{56}}$        

$\dfrac{{16}}{{56}};\dfrac{{35}}{{56}}$  

$\dfrac{{16}}{{56}};\dfrac{{35}}{{ - 56}}$      

$\dfrac{{ - 16}}{{56}};\dfrac{{ - 35}}{{56}}$

$\dfrac{1}{2}$                    

$\dfrac{6}{8}$          

$\dfrac{3}{4}$                 

$\dfrac{{ - 3}}{4}$