\(2x^2+2y^2=5xy\)
\(\Leftrightarrow2x^2+2y^2-4xy-xy=0\)
\(\Leftrightarrow2x\left(x-2y\right)-y\left(x-2y\right)=0\)
\(\Leftrightarrow\left(2x-y\right)\left(x-2y\right)=0\)
\(y>x>0\Leftrightarrow x-2y< 0\)
\(\Leftrightarrow2x-y=0\Leftrightarrow x=\dfrac{y}{2}\)
\(A=\dfrac{x+y}{x-y}=\dfrac{\dfrac{y}{2}+y}{\dfrac{y}{2}-y}=\dfrac{\dfrac{3}{2}y}{-\dfrac{y}{2}}=\dfrac{3}{2}:-\dfrac{1}{2}=-3\)