Question

Tìm x , y biết :

a / \(\dfrac{-5}{x}\)= \(\dfrac{y}{16}\) = \(\dfrac{-18}{72}\)

b / \(\dfrac{1}{2}\) = \(\dfrac{x-1}{8}\) = \(\dfrac{10}{y-5}\)

Answer 1

a/ \(\dfrac{-5}{x}\) = \(\dfrac{-18}{72}\)

\(\Rightarrow\dfrac{5}{x}=\dfrac{18}{72}=\dfrac{1}{4}\)

\(\Rightarrow x=5:\dfrac{1}{4}=20\)

\(\dfrac{y}{16}=\dfrac{-18}{72}\) \(=\dfrac{-1}{4}\)

\(\Leftrightarrow\) 4y = - 16

\(\Leftrightarrow\) y = -4

Vậy x = 20 ; y = -4

b/ \(\dfrac{1}{2}=\dfrac{x-1}{8}=\dfrac{10}{y-5}\)

\(\Rightarrow\dfrac{x-1}{8}=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{x-1}{8}=\dfrac{4}{8}\)

\(\Rightarrow x-1=4\)

\(\Rightarrow\) \(x=4+1\)

\(x=5\)

\(\dfrac{10}{y-5}=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{10}{y-5}=\dfrac{10}{20}\)

\(\Rightarrow\) \(y-5=20\)

\(\Rightarrow y=20+5\)

\(y=25\)

Vậy x = 5 ; y = 25

Answer 2

a)

\(-\dfrac{5}{x}=-\dfrac{18}{72}\\ \Leftrightarrow\dfrac{5}{x}=\dfrac{18}{72}=\dfrac{1}{4}\\ \Leftrightarrow x=20\)

\(\dfrac{y}{16}=\dfrac{-18}{72}=-\dfrac{1}{4}\\ \Leftrightarrow4y=-16\\ \Leftrightarrow y=-4\)

b)

\(\dfrac{x-1}{8}=\dfrac{1}{2}\Rightarrow\dfrac{x-1}{8}=\dfrac{4}{8}\Rightarrow x-1=4\Rightarrow x=5\)

\(\dfrac{10}{y-5}=\dfrac{1}{2}\Leftrightarrow y-5=20\Leftrightarrow y=25\)