first, f(x)=x(x-4)=x²-4x
using algebra
completeing the square
(x²-4x+4)-4
(x-2)²-4
f(x)=(x-2)²-4
the vertex is at (2,-4) and the axis of symmetry is x=2
that means that x=2 is the mirror line
that means any point that is d units from the axis of symmetry in a horizontal direction will also have a mirror point on the other side of x=2
sorry if confusing, but explanation is axis of symmetry is at x=2
