Question

Completing the square allows us to see the vertex of the quadratic equation's parabola. Explain why. 

Answer 1

Well the vertex is the highest or possibly lowest point in a quadratic equation, the part where it hits the curve. For example imagine this is your graph--> ∩.
This graph has its vertex at the top. So when we complete the square and find the zeroes we can then find where the graph meets in the middle thus finding our vertex.