\(ax+4>2x+a^2\)
\(\Leftrightarrow-a^2+ax-2x>-4\)
\(\Leftrightarrow-a^2+x\left(a-2\right)>-4\Leftrightarrow x\left(a-2\right)>a^2-4\)
+) Với a > 2 => \(x>\dfrac{a^2-4}{a-2}\Leftrightarrow x>a+2\)
+) Với a < 2 => \(x< \dfrac{a^2-4}{a-2}\Leftrightarrow x< a+2\)