Giải câu 1 trang 20 toán 6 tập 2 sgk chân trời sáng tạo

a)  ( $\frac{-2}{-5}$ : $\frac{3}{-4}$).$\frac{4}{5}$

=  ($\frac{-2}{-5}$ . $\frac{-4}{3}$) . $\frac{4}{5}$ = $\frac{-2.-4}{-5.3}$. $\frac{4}{5}$

= $\frac{-8}{15}$. $\frac{4}{5}$ = $\frac{-8.4}{15.5}$ = $\frac{-32}{75}$

b) $\frac{-3}{-4}$ : ($\frac{7}{-5}$.$\frac{-3}{2}$)

= $\frac{3}{4}$ : $\frac{7.-3}{-5.2}$ = $\frac{3}{4}$: $\frac{21}{10}$

= $\frac{3}{4}$.$\frac{10}{21}$ = $\frac{3.10}{4.21}$ = $\frac{30}{84}$

c)  $\frac{-1}{9}.\frac{-3}{5}+\frac{5}{-6}.\frac{-3}{5}+\frac{5}{2}.\frac{-3}{5}$

= $\frac{-3}{5}$. ($\frac{1}{9}$ + $\frac{-5}{6}$ + $\frac{5}{2}$)

= $\frac{-3}{5}$. ( $\frac{-2}{18}$ + $\frac{-15}{18}$ + $\frac{45}{18}$)

= $\frac{-3}{5}$. $\frac{-2-15+45}{18}$ =$\frac{-3}{5}$.$\frac{28}{18}$

= $\frac{-3.28}{5.18}$= $\frac{-84}{90}$