Question

Tìm x,y biết :

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

Answer 1

Áp dụng tc của DTSBN ta có

\(\dfrac{x}{3}=\dfrac{y}{5}=\dfrac{2x}{6}=\dfrac{5y}{25}=\dfrac{2x+5y}{6+25}=\dfrac{1}{31}\)

( do 2x + 5y = 1 )

Suy ra

\(\dfrac{2x}{6}=\dfrac{1}{31}\Rightarrow\dfrac{x}{3}=\dfrac{1}{31}\Rightarrow x=\dfrac{3}{31}\)

\(\dfrac{5y}{25}=\dfrac{1}{31}\Rightarrow\dfrac{y}{5}=\dfrac{1}{31}\Rightarrow y=\dfrac{5}{31}\)

Vậy ....

Answer 2

Theo t/c dãy tỉ số bằng nhau ta có :

\(\dfrac{x}{3}=\dfrac{y}{5}=\dfrac{2x}{6}=\dfrac{5y}{25}=\dfrac{2x+5y}{6+25}=\dfrac{1}{31}\)

\(\Rightarrow\left\{{}\begin{matrix}\dfrac{x}{3}=\dfrac{1}{31}\Rightarrow x=\dfrac{3.1}{31}=\dfrac{3}{31}\\\dfrac{y}{5}=\dfrac{1}{31}\Rightarrow y=\dfrac{5.1}{31}=\dfrac{5}{31}\end{matrix}\right.\)

Vậy........

Answer 3

ta có:

\(\dfrac{x}{3}=\dfrac{y}{5}=\dfrac{2x}{6}=\dfrac{5y}{25}\)

áp dụng tính chất dãy tỉ số bằng nhau :

ta có: \(\dfrac{2x}{6}=\dfrac{5y}{25}=\dfrac{2x-5y}{6-25}=\dfrac{1}{-19}\)

\(\Rightarrow\).............................

..............................

tự làm tiếp nhé