\(\frac{1+3y}{12}\)= \(\frac{1+5y}{5x}\)= \(\frac{1+7y}{4x}\)= \(\frac{1+3y+1+5y-1-7y}{12+5x-4x}\)= \(\frac{\left(1+1-1\right)+\left(3y+5y-7y\right)}{12+\left(5x-4x\right)}\)= \(\frac{3+y}{12+x}\)= \(\frac{15+5y}{60+5x}\)= \(\frac{1+5y}{5x}\)= \(\frac{15+5y}{60+5x}\)= \(\frac{15+5y-1-5y}{60+5x-5x}\)= \(\frac{14}{60}\)= \(\frac{7}{30}\).
=> \(\frac{1+3y}{12}\)= \(\frac{7}{30}\)=> 1 + 3y = \(\frac{7}{30}\). 12 = \(\frac{14}{5}\)
=> 3y = \(\frac{9}{5}\)=> y = \(\frac{9}{5}\): 3 = \(\frac{3}{5}\)
\(\frac{1+5y}{5x}\)= \(\frac{7}{30}\)=> 5x = (1 + 5y) : \(\frac{7}{30}\)= (1 + 5 . \(\frac{3}{5}\)) . \(\frac{30}{7}\)= 4 . \(\frac{70}{7}\)= \(\frac{120}{17}\)=> x = \(\frac{120}{17}\): 5 = \(\frac{24}{17}\)
Vậy x = \(\frac{24}{17}\); y = \(\frac{3}{5}\).
Chúc bạn học tốt !
Bạn Nguyễn Hoàng Vinh Sang giỏi quá làm đúng rồi
Bạn 
le thi phuong thao làm theo cách bạn ấy nha
Ai thấy mình nói đúng thì nha
\(\frac{1+3y}{12}=\frac{1+5y}{5x}=\frac{1+7y}{4x}=\frac{\left(1+3y\right)+\left(1+7y\right)}{12+4x}\)
=\(\frac{2+10y}{2.\left(6+2x\right)}=\frac{2.\left(1+5y\right)}{2.\left(6+2x\right)}=\frac{1+5y}{6+2x}\)
Vậy \(\frac{1+5y}{5x}=\frac{1+5y}{6+2x}\)
Ta có hai trường hợp:
TH1: 1+5y=0
=>y=-1/5
=>\(\frac{1+3.\frac{-1}{5}}{12}=0\)(vô lí)
TH2:5x=6+2x
=>3x=6
=>x=2
=>\(\frac{1+3y}{12}=\frac{1+5y}{5.2}\)
=>y=.....
Nguyễn Hoàng Vinh SAng xem lại giúp mk dòng thứ 2 sao 1+1-1=3 vậy
