Here h = 1, k = 1 and r = √2
The equation of circle is, (x–h)2+(y–k)2 = r2
∴ (x–1)2+(y–1)2 = (√2)2
⇒ x2 + 1 – 2x + y2 + 1 – 2y = 2 ⇒ x2+y2 – 2x – 2y = 0