This means our general form for this equation is
x^2/a^2 + y^2/b^2 = 1

The foci is the following sets of points:
(-c, 0) and (c, 0)

To find c,
c^2 = a^2 - b^2
The square root of 16 = 4 = a^2.
The square root of 4 = 2 = b^2
Then:
c^2 = 4 - 2
c^2 = 2
Take square root of both sides:
c = +2, -2
Then the following two points for the foci:
(2, 0) and (-2, 0)