Determine the type of curve represented by the equation
x2 / k + y2 / k - 16 = 1
In each of the following cases:
(a) k > 16,
(b) 0 < k < 16,
(c) k < 0.
(d) Show that all the curves in parts (a) and (b) have the same foci, no matter what the value of is.