A = $\frac{3}{5}$ . $\frac{4}{7}$ - $\frac{2}{7}$ . $\frac{3}{5}$ - $\frac{3}{5}$ . $\frac{6}{7}$
= $\frac{3}{5}$ . ($\frac{4}{7}$ - $\frac{2}{7}$ - $\frac{6}{7}$)
= $\frac{3}{5}$ . $\frac{-4}{7}$
= $\frac{-12}{35}$
B = $\frac{\frac{2}{7} + \frac{2}{5} + \frac{2}{17} - \frac{2}{293}}{\frac{3}{7} + \frac{3}{5} + \frac{3}{17} - \frac{3}{293} }$
= $\frac{2 . (\frac{1}{7} + \frac{1}{5} + \frac{1}{17} - \frac{1}{293})}{3 . (\frac{1}{7} + \frac{1}{5} + \frac{1}{17} - \frac{1}{293})}$
= $\frac{2}{3}$
Chúc học tốt!!!
