Question

x+y=-70 và y/x=5/9. Tìm x,y

Answer 1

 x + y = -70 => x = -70 - y

\(\frac{y}{x}=\frac{5}{9}\Rightarrow9y=5x\)

\(\Rightarrow9y=5\left(-70-y\right)\)

\(\Leftrightarrow9y=-350-5y\)

\(\Leftrightarrow9y+5y=-350\)

\(\Leftrightarrow14y=-350\)

\(\Leftrightarrow y=-25\)

\(\Rightarrow x=-70-\left(-25\right)=-45\)

Answer 2

Ta có : \(\frac{y}{x}=\frac{5}{9}\Leftrightarrow5x-9y=0\)

Ta có hệ : \(\hept{\begin{cases}5x-9y=0\\x+y=-70\end{cases}\Leftrightarrow\hept{\begin{cases}5x-9y=0\\5x+5y=-350\end{cases}\Leftrightarrow}\hept{\begin{cases}-14y=350\\x+y=-70\end{cases}}}\)

\(\Leftrightarrow y=-25\Rightarrow x=-45\)