Giải bài 4 trang 33

Đề bài

Tìm x biết:

a) $\frac{7}{-8}-x=\frac{-4}{5}:\frac{3}{10}$

b) $\frac{-5}{6}.x=\frac{-5}{8}-1\frac{3}{4}$

Lời giải chi tiết

a)

 $\begin{array}{c}\frac{7}{-8}-x=\frac{-4}{5}:\frac{3}{10}\\ \frac{7}{-8}-x=\frac{-4}{5}.\frac{10}{3}\\ \frac{7}{-8}-x=\frac{-8}{3}\\ x=\frac{7}{-8}-\frac{-8}{3}\\ x=\frac{43}{24}.\end{array}$

b)

 $\begin{array}{c}\frac{-5}{6}.x=\frac{-5}{8}-1\frac{3}{4}\\ \frac{-5}{6}.x=\frac{-5}{8}-\frac{7}{4}\\ \frac{-5}{6}.x=\frac{-19}{8}\\ x=\frac{-19}{8}:\frac{-5}{6}\\ x=\frac{57}{20}.\end{array}$