Question

\(\dfrac{5x}{7y}\)=\(\dfrac{-1}{3}\)và -2x+3y=7

Answer 1

Ta có\(\dfrac{5x}{7y}=\dfrac{-1}{3}\Leftrightarrow\dfrac{x}{y}=\dfrac{-7}{15}\Leftrightarrow\dfrac{x}{-7}=\dfrac{y}{15}\)

Áp dụng dãy tỉ số bằng nhau 

\(\dfrac{x}{-7}=\dfrac{y}{15}=\dfrac{-2x}{14}=\dfrac{3y}{45}=\dfrac{-2x+3y}{14+45}=\dfrac{7}{59}\)

\(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{x}{-7}=\dfrac{7}{59}\\\dfrac{y}{15}=\dfrac{7}{59}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-\dfrac{49}{59}\\y=\dfrac{105}{59}\end{matrix}\right.\)