Question 880898
You need to complete the square. Once you do that then the parabola will be in vertex form. The vertex lies on the axis of symmetry.
Example: Find the axis of symmetry of {{{y=x^2+4x}}}
{{{y=x^2+4x}}}
{{{y=x^2+4x+4-4}}}
{{{y=(x+2)^2-4}}}
Now it's in vertex form. The vertex is (-2,-4).
The axis of symmetry is {{{x=-2}}}.
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{{{drawing(300,300,-5,5,-5,5,grid(1),blue(line(-2,-10,-2,10)),circle(-2,-4,0.3),graph(300,300,-5,5,-5,5,x^2+4x))}}}