Draw the graph with the following equation, choosing appropriate values for x. For the graph, write down the equation of line of symmetry.

$\displaystyle y=2x^2-3x-4$

I couldn't factorise it, and when I completed the square I got $\displaystyle x=4$ or $\displaystyle x=-1$. Then I tried quadratic formula and got $\displaystyle x=\frac{3\pm\sqrt{41}}{4}$. Therefore I got the line of symmetry to be 3. However, the line of symmetry is $\displaystyle \frac{3}{4}$ so I must have done something wrong =\ .