Math (URGENT)
posted by John on .
How to graph:
y=x(x4)
Calculator shows the vertex at (2,4)
Can someone explain why? Thanks.

Try completing the square.
x(x4) = x^2 4x +4 4
= (x2)^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.