The equation of a circle is (x-a) 2+(y- 1+a) 2 = 2.

Expansion formula: x2+y2-2ax+2 (a-1) y+a2+(a-1) 2-2 = 0.

So there is: a 2+(a-1) 2-2 = 3.

a^2-a-2=0

(a-2)(a+ 1)=0

So there is a =- 1.

So the equation of the circle is: x 2+y 2+2x-4y+3 = 0.