sai 5: Thực hiện các phép tính nhân chia sau: (-1)/(4)cdot (5)/(7) 2) (-3)/(8)cdot (16)/(9) 3) (-5)/(3)cdot (-9) 4) (3)/(-10)cdot (-(-15)/(4)) D (-5)/(6):(2)/(3) 6) (-4)/(7):(-1)/(3) 7) -10:(2)/(3) 8) (-3)/(-5):(-5) (21)/(25)cdot (11)/(9)cdot (5)/(7) 10) (3)/(5):((1)/(2)cdot (3)/(5))

1) $\frac{-1}{4} \cdot \frac{5}{7} = \frac{-1 \cdot 5}{4 \cdot 7} = \frac{-5}{28}$<br /><br />2) $\frac{-3}{8} \cdot \frac{16}{9} = \frac{-3 \cdot 16}{8 \cdot 9} = \frac{-3 \cdot 2}{9} = \frac{-6}{9} = \frac{-2}{3}$<br /><br />3) $\frac{-5}{3} \cdot (-9) = \frac{-5 \cdot (-9)}{3} = \frac{45}{3} = 15$<br /><br />4) $\frac{3}{-10} \cdot (-\frac{-15}{4}) = \frac{3}{-10} \cdot \frac{15}{4} = \frac{3 \cdot 15}{-10 \cdot 4} = \frac{45}{-40} = \frac{-9}{8}$<br /><br />5) $\frac{-5}{6} : \frac{2}{3} = \frac{-5}{6} \cdot \frac{3}{2} = \frac{-5 \cdot 3}{6 \cdot 2} = \frac{-15}{12} = \frac{-5}{4}$<br /><br />6) $\frac{-4}{7} : \frac{-1}{3} = \frac{-4}{7} \cdot \frac{3}{-1} = \frac{-4 \cdot 3}{7 \cdot (-1)} = \frac{-12}{-7} = \frac{12}{7}$<br /><br />7) $-10 : \frac{2}{3} = -10 \cdot \frac{3}{2} = \frac{-10 \cdot 3}{2} = \frac{-30}{2} = -15$<br /><br />8) $\frac{-3}{-5} : (-5) = \frac{3}{5} \cdot \frac{1}{-5} = \frac{3}{-25} = \frac{-3}{25}$<br /><br />9) $\frac{21}{25} \cdot \frac{11}{9} \cdot \frac{5}{7} = \frac{21 \cdot 11 \cdot 5}{25 \cdot 9 \cdot 7} = \frac{3 \cdot 11}{5 \cdot 9} = \frac{11}{15}$<br /><br />10) $\frac{3}{5} : (\frac{1}{2} \cdot \frac{3}{5}) = \frac{3}{5} : \frac{3}{10} = \frac{3}{5} \cdot \frac{10}{3} = \frac{3 \cdot 10}{5 \cdot 3} = 2$<br />