\(\left(\dfrac{2}{9}+\dfrac{5}{9}\right)+\dfrac{1}{9}=\dfrac{7}{9}+\dfrac{1}{9}=\dfrac{7+1}{9}=\dfrac{8}{9}\)
\(\dfrac{2}{9}+\left(\dfrac{5}{9}+\dfrac{1}{9}\right)=\dfrac{2}{9}+\dfrac{6}{9}=\dfrac{2+6}{9}=\dfrac{8}{9}\)
\(\dfrac{2}{9}+\dfrac{5}{9}+\dfrac{1}{9}=\dfrac{2+5+1}{9}=\dfrac{8}{9}\)
Các biểu thức trên bằng nhau và cùng bằng \(\dfrac{8}{9}\)
(\(\dfrac{2}{9}\)+ \(\dfrac{5}{9}\)) + \(\dfrac{1}{9}\) = \(\dfrac{8}{9}\)
\(\dfrac{2}{9}\) + (\(\dfrac{5}{9}\) + \(\dfrac{1}{9}\)) = \(\dfrac{8}{9}\)
\(\dfrac{2}{9}\) + \(\dfrac{5}{9}\) + \(\dfrac{1}{9}\) =\(\dfrac{8}{9}\)
