Y = (x-4) (x+20) find vertex

Y = (x-4) (x+20) = = = > 0 = (x-4) (x+20)

that means the roots of that quadratic are x = 4 and x = - 20.

now, the vertex will be between these two guys, right in between.

from - 20 to 4 there are 24 units, half-way of that is 12 units, so, if we move from - 20, 12 units to the right or towards 4, we'll end up at - 20 + 12 = - 8.

so, the vertex's x-coordinate is - 8 then, what's "y" anyway?

y = (x-4) (x+20) x = - 8

y = [ (-8) - 4] [ (-8) + 20]

y = (-12) (12)

y = - 144

therefore, the vertex is at (-8, - 144)