The axis of symmetry of a parabola is the vertical line passing through its vertex. Given a parabola [tex] ax^2+bx+c=0 [/tex], the vertex x-coordinate can be found using
[tex] x = -\dfrac{b}{2a} [/tex]
In your case, the formula leads to
[tex] x = -\dfrac{40}{10} = -4 [/tex]
So, this parabola is symmetric with respect to the line [tex] x = -4 [/tex]
