Show that the maximum values of the electric field |E| for points on the axis of a

Question:

Show that the maximum values of the electric field |E| for points on the axis of a uniform ring of charge q and radius a occur at a distance
x = ± a/√2.
If an electron is placed at the centre of the ring and is then displaced a small distance x along the axis (x << a), show that it oscillates with a frequency
v = √eq/16π3ε0a3m
Where m is the mass of the electron.