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) $\frac{1}{6}+\frac{5}{7}:x = \frac{-7}{18}$.
$\Leftrightarrow \frac{5}{7}:x = \frac{-7}{18} - \frac{1}{6}$.
$\Leftrightarrow \frac{5}{7}:x = \frac{-7}{18} - \frac{3}{18}$.
$\Leftrightarrow \frac{5}{7}:x = \frac{-10}{18}$.
$\Leftrightarrow \frac{5}{7}:x = \frac{-5}{9}$.
$\Leftrightarrow x = \frac{5}{7}:\frac{-5}{9}$.
$\Leftrightarrow x = \frac{5}{7}\times \frac{-9}{5}$.
$\Leftrightarrow x = \frac{-9}{7}$.