a) \(\dfrac{x}{15}=\dfrac{7}{5}\)
Ta có: 15 = 5 . 2
\(\Rightarrow\) x = 7 . 2
Vậy x = 14.
b) \(\dfrac{14}{x}=\dfrac{7}{5}\)
Ta có: 14 = 7 . 2
\(\Rightarrow\) x = 5 . 2
Vậy x = 10.
c) \(\dfrac{2}{3}:\dfrac{1}{3}x=\dfrac{7}{5}:\dfrac{4}{5}\)
\(\dfrac{2}{3}:\dfrac{1}{3}x=\dfrac{7}{4}\)
\(\dfrac{1}{3}x=\dfrac{2}{3}:\dfrac{7}{4}\)
\(\dfrac{1}{3}x=\dfrac{8}{21}\)
\(x=\dfrac{8}{21}:\dfrac{1}{3}\)
\(x=\dfrac{8}{7}\) .
Áp dụng tính chất \(\dfrac{a}{b}=\dfrac{c}{d}\Rightarrow ad=bc\)
a)\(\dfrac{x}{15}=\dfrac{7}{5}\Rightarrow5x=15.7\Rightarrow5x=105\Rightarrow5x=5.21\Rightarrow x=21\)
b)\(\dfrac{14}{x}=\dfrac{7}{5}\Rightarrow7x=14.5\Rightarrow7x=70\Rightarrow7x=7.10\Rightarrow x=10\)
c)\(\dfrac{2}{3}:\dfrac{1}{3}x=\dfrac{7}{5}:\dfrac{4}{5}\Rightarrow\dfrac{2}{3}.\dfrac{3}{x}=\dfrac{7}{5}.\dfrac{5}{4}\Rightarrow\dfrac{2}{x}=\dfrac{7}{4}\Rightarrow7x=2.4\Rightarrow7x=8\Rightarrow x=\dfrac{8}{7}\)
