we know that
The equation of a vertical parabola in vertex form is equal to

where
(h,k) is the vertex
if
-----> then the parabola open upward (the vertex is a minimum)
if
-----> then the parabola open downward (the vertex is a maximum)
The axis of symmetry is equal to

In this problem let's analyze two cases
First case

the vertex is the point 

so
-----> then the parabola open upward (the vertex is a minimum)
The axis of symmetry is equal to

Second case

the vertex is the point 

so
-----> then the parabola open upward (the vertex is a minimum)
The axis of symmetry is equal to
