posted by John .
How to graph:
Calculator shows the vertex at (2,-4)
Can someone explain why? Thanks.
Try completing the square.
x(x-4) = x^2 -4x +4 -4
= (x-2)^2 - 4
The vertex is the lowest point of the parabolic curve. That is obviously where x = 2, where the first term is zero.
The value of y there is -4.