Start with the ellipse in standard form
If the ellipse is ((x-h)^2/a^2 + (y-k)^2/b^2 = 1) and (a > b), the major axis is horizontal
If the ellipse is ((x-h)^2/b^2 + (y-k)^2/a^2 = 1) and (a > b), the major axis is vertical
Compute (c) using (c^2 = a^2 – b^2)
For a horizontal ellipse, the foci are ((h-c, k)) and ((h+c, k))
For a vertical ellipse, the foci are ((h, k-c)) and ((h, k+c))
If the ellipse is centered at the origin, use (h = 0) and (k = 0)
If the ellipse is not in standard form, rewrite it into standard form first