The axis of simetry of a parabola is the vertical line that cross the vertex of the parabola.
So, we need to find the x-value of the vertex:
[tex]\begin{gathered} \text{The general equation of a parabola is:} \\ y=ax^2+bx+c \\ \text{The x-value of the vertex is:} \\ x_v=-\frac{b}{2a} \end{gathered}[/tex]So, in this case a=1 and b=8:
[tex]x_v=-\frac{8}{2\cdot1}=-4_{}[/tex]The axis of simetry is x=-4.
