So the equation of the red graph is already given to us:
. I assume you meant the blue graph?
We can use the vertex form:
, where
is the vertex. (We can ignore
because
is 1 for this graph.) Remember that the vertex is the maximum or minimum of a parabola and the point that the line of symmetry passes through. For f(x) the vertex is (0,0).
The vertex for
is at
on the coordinate plane. (4 left, 2 down)
Plug into the vertex form:
The double negative becomes a positive, and then you're done: