\(\dfrac{1}{x}+\dfrac{y}{4}=\dfrac{5}{4}\)
\(\Leftrightarrow\dfrac{4}{4x}+\dfrac{xy}{4x}=\dfrac{5}{4}\)
\(\Leftrightarrow\dfrac{4+xy}{4x}=\dfrac{5}{4}\)
\(\Leftrightarrow4\left(4+xy\right)=5.4x\)
\(\Leftrightarrow16+4xy=20x\)
\(\Leftrightarrow16+y=16x\)
Tịt!