Question

What is the vertex and x-intercepts of y=(x+4)(x-2) ?

Answer 1

First plot it
http://www.wolframalpha.com/input/?i=plot++%28x%2B4%29%28x-2%29+

Answer 2

The x-coordinate of the vertex is the midpoint of the points where the parabola intersects the x-axis

Answer 3

It is the midpoint (-4,0) and (2,0) so it is (-1,0)
replace x by -1, you get the y-coordinate of the vertex

Answer 4

The vertex is (-1,-9)