Question

Tìm x, y biết  (1+3y)/12=(1+5y)/5x=(1+7y)/4x

Answer 1

Lời giải:
$\frac{1+5y}{5x}=\frac{1+7y}{4x}$

$\Rightarrow \frac{1+5y}{5}=\frac{1+7y}{4}$

$\Rightarrow 4(1+5y)=5(1+7y)$
$\Rightarrow 4+20y=5+35y$

$\Rightarrow 15y=-1\Rightarrow y=\frac{-1}{15}$

Khi đó:

$\frac{1+3y}{12}=\frac{1+5y}{5x}$

$\Rightarrow x=\frac{12(1+5y)}{5(1+3y)}=\frac{12(1+5.\frac{-1}{15})}{5(1+3.\frac{-1}{15})}=2$