Giải bài 1 trang 20

Đề bài

Tính giá trị của biểu thức.

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

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

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

Lời giải chi tiết

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

$=\left(\frac{2}{5}.\frac{-4}{3}\right).\frac{4}{5}=\frac{-8}{15}.\frac{4}{5}=\frac{-32}{75}$

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

$=\frac{3}{4}:\frac{-21}{-10}=\frac{3}{4}.\frac{10}{21}=\frac{30}{84}=\frac{5}{14}$

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

$=\frac{-3}{5}.\left(\frac{-1}{9}+\frac{5}{-6}+\frac{5}{2}\right)=\frac{-3}{5}.\left(\frac{-2}{18}+\frac{-15}{18}+\frac{45}{18}\right)=\frac{-3}{5}.\frac{28}{18}=\frac{-3}{5}.\frac{14}{9}=\frac{-14}{15}$

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