Me solve this problem. i really need .

When:
a = b = 0 we have point (0,0).
a = 0 and b ≠ 0 vertical line segment from (0, -b) to (0, b)
a ≠ 0 and b = 0 horizontal line segment from (-a, 0) to (a, 0)
a ≠ 0 and b ≠ 0 a ≠ b ellipse
a ≠ 0 and b ≠ 0 a = b circle