Hi there, the axis of symmetry can be found by transforming a parabola into turning point form. When you know the turning point i.e (a,b) then axis of symmetry is simply x=a.

Your first equation is not a parabola. Equations 2 & 3 are pretty much in turning point form, equation 4 can be put into turning point form by completing the square.

http://en.wikipedia.org/wiki/Parabola