Vertical parabolas give an important piece of information: When the parabola opens up, the vertex is the lowest point on the graph — called the minimum, or min. When the parabola opens down, the vertex is the highest point on the graph — called the maximum, or max.
The y coordinate of the vertex tells you the highest or lowest point, depending on whether the parabola opens downward or upward.
For something like y = -2(x-5)^2 + 10, it opens downward and has the vertex at (5,10). The highest point is (5,10) so the largest y value or output is y = 10. This is the maximum of the function. Note the value of 'a' is a = -2 which is negative. Also note the vertex form y = a(x-h)^2 + k with vertex (h,k).
For an example like y = 7(x+2)^2 - 8 we have a = 7 so the parabola opens upward meaning we'll have a minimum this time. The lowest point is the vertex (h,k) = (-2,-8). The minimum of the function is y = -8.
