Graph ​ f(x)=(x+2)(x−4)

(x + 2)(x - 4)     expand

x^2 + 2x - 4x - 8

x^2 - 2x - 8

The x coordinate of the vertex is  -(-2) / (2 * 1)  =   2 /2  = 1

The y coordinate of the vertex is  (1)^2 - 2(1) - 8  =  1 - 2 - 8  =  -9

So...the vertex is (1, - 9)

A second point can be found if we let x = 0

(0)^2 - 2(0) - 8  =

-8

So  (0, - 8)  is on the graph

Here's the graph :  https://www.desmos.com/calculator/tgpdpinlno

thanks you