Question 634613
<pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
y=x^2+6x+c
The value of c for which the vertex of the parabola will lie on the x-axis
y = (x - 3)^2 - 9  + c   |comleting the Square to put into Vertex form for:  V(-3,0)
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
  c = 9    and {{{y = (x-3)^2}}}
{{{drawing(300,300,   -6, 6, -6, 6,  blue(line(3,6,3,-6))  , grid(1),
circle(3, 0,0.3),
graph( 300, 300, -6, 6, -6, 6,0,(x-3)^2 ))}}}