(3x-y)/(x+y)=3/4

Nhân chéo lên ta dc:

12x-4y=3x+3y <=> 9x=7y

=> x/y=7/9

Ta có : \(\frac{3x-y}{x+y}=\frac{3}{4}\)

=>  (3x - y) . 4 = (x + y) . 3

=> 12x - 4y = 3x + 3y

=> 12x - 3x = 3y + 4y

         9x     =     7y

=> \(\frac{x}{y}=\frac{7}{9}\)

                 Vậy tỉ số \(\frac{x}{y}\)là \(\frac{7}{9}\)

         Nếu đúng thì nhớ **** cho mình nha ^_^  !

x=7

y=9  đúng nhưng ko cs điểm tối đa

3x - y/x+y = 3/4

=> 4(3x - y) = 3(x + y)

=> 12x - 4y = 3x + 3y

=> 12x - 3x = 3y + 4y

=> 9x = 7y

=> x/y = 7/9

\(\frac{3x-y}{x+y}=\frac{3}{4}\Rightarrow12x-4y=3x+3y\Leftrightarrow9x-7y=0\Leftrightarrow x=\frac{7y}{9}\)

Khi đó \(\frac{x}{y}=\frac{\frac{7}{9}y}{y}=\frac{7}{9}\)

nha bạn chúc bạn học tốt 

\(\frac{3x-y}{x+y}=\frac{3}{4}\Rightarrow12x-4y=3x+3y\)

\(\Leftrightarrow9x=7y\Leftrightarrow\frac{x}{y}=\frac{7}{9}\)

có nhiều người nói x/y=7/9

=> x=7;y=9 là sai bn nhé

\(\frac{3x-y}{x+y}=\frac{3}{4}\)

\(\Rightarrow\left(3x-y\right).4=\left(x+y\right).3\)

\(\Rightarrow12x-4y=3x+3y\)

\(\Rightarrow12x-3x=3y+4y\)

\(\Rightarrow9x=7y\)

\(\Rightarrow\frac{x}{y}=\frac{7}{9}\)

3x-y/y+x=34

=> 3x - y = 34 ( y + x )

=>3x - y = 34y + 34x

=>-35y = 31x

=>x/y = -35/31

\(\Rightarrow4\left(3x+5y\right)=x-2y\Rightarrow12x+20y=x-2y\Rightarrow11x=-22y\Rightarrow\frac{x}{y}=\frac{-22}{11}=-2\)

\(\frac{3x+5y}{x-2y}=\frac{1}{4}\)

\(\Rightarrow x-2y=4\left(3x+5y\right)\)

\(\Rightarrow x-2y=12x+20y\)

\(\Rightarrow12x-x=20y+2y\)

\(\Rightarrow11x=22y\)

\(\Rightarrow x=2y\Leftrightarrow\frac{x}{y}=2\)

Ta có: (3x-y)/(x+y) = 3/4 =>4(3x-y)=3(x+y)

                                   =>12x-4y=3x+3y

                                   =>12x-3x=3y+4y

                                   =>9x=7y

=>x/y=7/9

vậy x/y=7/9

bài 1

\(\frac{3x-y}{x+y}=\frac{3}{4}\)

\(\Rightarrow\left(3x-y\right).4=\left(x+y\right)3\)

\(\Rightarrow12x-4y=3x+3y\)

\(\Rightarrow9x=7y\)

\(\Rightarrow\frac{x}{y}=\frac{7}{9}\)

Vậy \(\frac{x}{y}=\frac{7}{9}\)

bài 2

\(\frac{3x+2}{5x+7}=\frac{3x-1}{5x+4}\)

\(\Rightarrow\) \(\left(3x+1\right)\left(5x+4\right)=\left(3x-1\right)\left(5x+7\right)\)

\(\Rightarrow15x^2+12x+10x+8=15x^2+21x-5x-7\)

\(\Rightarrow22x+8=16x-7\)

\(\Rightarrow22x+16x=-7-8\)

\(\Rightarrow6x=-15\)

\(\Rightarrow x=-2,5\)

Vậy x=-2,5