Tính giá trị các biểu thức sau một...

- Hướng dẫn giải

$\begin{array}{l}a)A=\frac{5}{11}.\frac{5}{7}+\frac{5}{11}.\frac{2}{7}+\frac{6}{11}=\frac{5}{11}.\left(\frac{5}{7}+\frac{2}{7}\right)+\frac{6}{11}=\frac{5}{11}+\frac{6}{11}=1\\ \end{array}$

$\begin{array}{l}b)B=\frac{3}{13}.\frac{6}{11}+\frac{3}{13}.\frac{9}{11}-\frac{3}{13}.\frac{4}{11}\\ \\ =\frac{3}{13}.\left(\frac{6}{11}+\frac{9}{11}-\frac{4}{11}\right)=\frac{3}{13}.\frac{11}{11}.\\ \\ c)C=\left(\frac{12}{61}-\frac{31}{22}+\frac{14}{91}\right)\left(\frac{3}{6}-\frac{2}{6}-\frac{1}{6}\right)\\ \\ =\left(\frac{12}{61}-\frac{31}{22}+\frac{14}{91}\right).0=0\end{array}$