Tìm x, biết:
Bài 5: Tìm x, biết:
a) $x\times \frac{21}{25}=\frac{-7}{10}$
b) $\frac{-3}{20}x=\frac{5}{12}-\frac{2}{5}$
c) $\frac{2}{9}/x=\frac{1}{18}/0.375$
d) $(-\frac{11}{12})/2x=\frac{5}{2}+\frac{1}{4}$
a) $x\times \frac{21}{25}=\frac{-7}{10}$ suy ra $x=(\frac{-7}{10}/\frac{21}{25}=\frac{-5}{6}$
b) $\frac{-3}{20}x=\frac{5}{12}-\frac{2}{5}$ suy ra $x=\frac{1}{60}/(\frac{-3}{20})=\frac{-1}{9}$
c) $\frac{2}{9}/x=\frac{1}{18}/0.375$ suy ra $x=\frac{2}{9}/\frac{4}{27}=\frac{3}{2}$
d) $(-\frac{11}{12})/2x=\frac{5}{2}+\frac{1}{4}$
$(-\frac{11}{12})/2x=\frac{11}{4}$ suy ra $2x= (\frac{-11}{12})/\frac{11}{4}$ nên $x=\frac{-1}{6}$
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