Can someone explain

Hello jxc! You know me (flec from aops)

Graphing quadratics can actually be very simple.

Let's use an example.

$y=x^2+6x+9$

We plug in y as 0 to get the x-intercepts

Now for the vertex.

Vertex form is y = a(x – h)2 + k, where (h,k) is the vertex.

We rearrange $y=x^2+6x+9$ to get it in this form, and we get the vertex.

Plot the vertex and two x-intercepts and you will get your parabola!