Do \(2y^2-x^2=1\)
\(\Rightarrow2x^3-y^3=\left(2y-x\right)\left(2y^2-x^2\right)\)
\(\Leftrightarrow2x^3-y^3=4y^3-2yx^2-2y^2x+x^3\)
\(\Leftrightarrow x^3+2yx^2+2y^2x-5y^3=0\)
\(\Leftrightarrow\left(x-y\right)\left(x^2+3xy+5y^2\right)=0\)
\(\Rightarrow x=y\)
easy from here