Question

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

Answer 1

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)