so first you would use the formula -b / 2a to find the x coordinate and then plug in the x coordinate in to x to find the y coordinate.
-8 / 2 = -4
y = (-4)^2 + 8 * -4 + 7
y = 16 + -32 + 7
y = -9
minimum value = -9
it is the y of the coordinate because value is the number the whole equation equals.