Here h = –a, k = –b and r = √a2−b2
The equation of circle is, (x–h)2+(y–k)2 = r2
∴ (x+a)2+(y+b)2 = (√a2−b2)2
⇒ x2+a2 + 2ax + y2+b2 + 2by = a2–b2 ⇒ x2+y2 + 2ax + 2by + 2b2 = 0