Giải câu 3 trang 37 sách toán VNEN lớp 6 tập 2

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Câu 3: Trang 37 sách toán VNEN lớp 6 tập 2

Tìm x, biết:

a) $\frac{4}{9}\times x = \frac{1}{9}$ .

b) $x:\frac{-1}{12} = \frac{7}{12}$ ;

c) $\frac{-5}{14}:x = \frac{-3}{10}$ .

d) $\frac{7}{18}\times x - \frac{2}{3} = \frac{5}{18}$ ;

e) $\frac{4}{9} - \frac{7}{8}\times x = \frac{-2}{3}$ .

f) $\frac{1}{6}+\frac{5}{7}:x = \frac{-7}{18}$ .

Bài làm:

a) $\frac{4}{9}\times x = \frac{1}{9}$ .

$\Leftrightarrow x = \frac{1}{9}:\frac{4}{9}$

$\Leftrightarrow x = \frac{1}{9}\times \frac{9}{4}$

$\Leftrightarrow x = \frac{1}{4}$ .

b) $x:\frac{-1}{12} = \frac{7}{12}$ ;

$\Leftrightarrow x = \frac{7}{12}\times \frac{-1}{12}$

$\Leftrightarrow x = \frac{-7}{144}$ .

c) $\frac{-5}{14}:x = \frac{-3}{10}$ .

$\Leftrightarrow x = \frac{-5}{14}:\frac{-3}{10}$

$\Leftrightarrow x = \frac{-5}{14}\times \frac{-10}{3}$

$\Leftrightarrow x = \frac{25}{21}$

d) $\frac{7}{18}\times x - \frac{2}{3} = \frac{5}{18}$ ;

$\Leftrightarrow \frac{7}{18}\times x = \frac{5}{18} + \frac{2}{3}$ ;

$\Leftrightarrow \frac{7}{18}\times x = \frac{5}{18} + \frac{12}{18}$ ;

$\Leftrightarrow \frac{7}{18}\times x = \frac{17}{18}$ ;

$\Leftrightarrow x = \frac{17}{18} : \frac{7}{18}$

$\Leftrightarrow x = \frac{17}{18} \times \frac{18}{7}$

$\Leftrightarrow x = \frac{17}{7}$

e) $\frac{4}{9} - \frac{7}{8}\times x = \frac{-2}{3}$ .

$\Leftrightarrow \frac{7}{8}\times x = \frac{4}{9} + \frac{2}{3}$

$\Leftrightarrow \frac{7}{8}\times x = \frac{4}{9} + \frac{6}{9}$

$\Leftrightarrow \frac{7}{8}\times x = \frac{10}{9}$

$\Leftrightarrow x = \frac{10}{9}:\frac{7}{8}$

$\Leftrightarrow x = \frac{10}{9}\times \frac{8}{7}$ .

$\Leftrightarrow x = \frac{80}{63}$ .

f) $\frac{1}{6}+\frac{5}{7}:x = \frac{-7}{18}$ .

$\Leftrightarrow \frac{5}{7}:x = \frac{-7}{18} - \frac{1}{6}$ .

$\Leftrightarrow \frac{5}{7}:x = \frac{-7}{18} - \frac{3}{18}$ .

$\Leftrightarrow \frac{5}{7}:x = \frac{-10}{18}$ .

$\Leftrightarrow \frac{5}{7}:x = \frac{-5}{9}$ .

$\Leftrightarrow x = \frac{5}{7}:\frac{-5}{9}$ .

$\Leftrightarrow x = \frac{5}{7}\times \frac{-9}{5}$ .

$\Leftrightarrow x = \frac{-9}{7}$ .

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Cập nhật: 07/09/2021

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