Tính: a) A = 5/11 . (-3/23). 11/5 . (-4,6); b) B = (-7/9) . 13/25 - 13/25 . 2/9

* Hướng dẫn giải

a)

 $$\begin{gathered} A=\frac{5}{11}\cdot \left(\frac{-3}{23}\right)\cdot \frac{11}{5}\cdot (-4,6) \\ =\frac{5}{11}\cdot \left(\frac{-3}{23}\right)\cdot \frac{11}{5}\cdot \left(\frac{-46}{10}\right)=\left(\frac{5}{11}\cdot \frac{11}{5}\right)\cdot \left(\frac{-3}{23}\right)\cdot \left(\frac{-46}{10}\right) \\ =1.\left(\frac{-3}{23}\right)\cdot \left(\frac{-23}{5}\right)=\frac{\left(-3\right).(-23)}{23.5}=\frac{3}{5} \end{gathered}$$

b) 

$$\begin{gathered} B=\left(-\frac{7}{9}\right)\cdot \frac{13}{25}-\frac{13}{25}\cdot \frac{2}{9} \\ =\frac{13}{25}\cdot \left[\left(-\frac{7}{9}\right)-\frac{2}{9}\right]=\frac{13}{25}\cdot (-1)=\frac{-13}{25} \end{gathered}$$