that's -{(x)(x)+4x} = -x(x+4).
When it's factorised the x axis intercepts are obvious.
That is zero when x is 0 or -4.
Set x = 0 for the y intercept so y intercept is the origin.
Two ways for the vertex.
Slope of the tangent =0 so derivative is zero so -2x-4 is 0 so x = -2 and f(-2) is 4.
Or, the vertex is midway above the x intercepts, which is halfway between 0 and -4, which is -2.
This is because the graph is parabolic and is symmetrical about the vertex vertical axis.
So again, you get f(-2) for the height of the maximum above the x axis
