The equation of a curve is $y=ax^2+5x+a-5$, where $a$ is a constant. In the case where $a=2$, find the set of values of $x$ for which the curve lies completely above the line $y=9$.
I sub $a=2$ and solve using simultaneous equation and get $x=1.5$ and $x=-4$ but I got confused as there is no intersection.