You can
put this solution on YOUR website!find the roots of the equation ie where the curve crosses the x-axis (where y=0). This is done by factorisation or using the quadrativ formula.
Once you have these two points, then the line of symmetry is mid way between them ,since a quadrativ is a symmetrical curve.
So, if the root are at x=1 and x=5, then the line of symmetry is at x=3.
Jon