y=3x^2-x+2
Find when the velocity, dy/dx, is equal to zero, this value of x will represent the axis of symmetry for a quadratic because all quadratics have a constant acceleration, and thus when dy/dx=0, y(x), is at either a global maximum or minimum...
dy/dx=6x-1
6x-1=0
6x=1
x=1/6
So the vertical line x=1/6 is the axis of symmetry.