Question 323622
The equation is already in vertex form, {{{y=a(x-h)^2+k}}}, where (h,k) is the vertex.
(h,k)=(-1,0)
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The vertex lies on the axis of symmetry.
{{{x=-1}}}
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{{{drawing(300,300,-5,5,-5,5,grid(1),circle(-1,0,.2),blue(line(-1,10,-1,-10)),graph(300,300,-5,5,-5,5,-3(x+1)^2))}}}