Question 652689
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Hi,
the vertex form of a Parabola opening up(a>0) or down(a<0), {{{y=a(x-h)^2 +k}}} 
where(h,k) is the vertex  and  x = h  is the Line of Symmetry

Parabola opening Downward a = -1 < 0
y= -x^2+1  V(0,1) x = 0 the line of symmetry &  When y = 0,  x = ± 1 
{{{drawing(300,300,   -6, 6, -6, 6, grid(1),
circle(0, 1,0.2),
circle(1, 0,0.2),
circle(-1, 0,0.2),
graph( 300, 300, -6, 6, -6, 6,0,-x^2+1 ))}}}