\(\Leftrightarrow yx^2+2yx+3y=3x^2+10x+20\)
\(\Leftrightarrow\left(y-3\right)x^2+2\left(y-5\right)x+3y-20=0\)
\(\Delta'=\left(y-5\right)^2-\left(y-3\right)\left(3y-20\right)\ge0\)
\(\Leftrightarrow-2y^2+19y-35\ge0\Rightarrow\frac{5}{2}\le y\le7\)
\(\Rightarrow y_{max}=7\) khi \(x=-\frac{1}{2}\)
\(y_{min}=\frac{5}{2}\) khi \(x=-5\)