Question 73164
Find the maximum or minimum value of y=(x+9)(x-9) and determine for which value of x it occurs 
:
Just think about it. You know that the parabola crosses the x axis(y=0) at + 9 and
-9.  The vertex will be half-way between these two points, Halfway between +9 and -9 is 0, right? So the value of x that the minimum occurs is 0