Answer :
[tex]The\ equation\ of\ the\ circle:(x-a)^2+(y-b)^2=r^2\\\\(a;\ b)-the\ center;\ r-the\ radius\\-------------------------\\\\(1;\ 2)\to a=1\ and\ b=2;\ r=2\\\\subtitute:\\\\(x-1)^2+(y-2)^2=2^2\\\\\boxed{(x-1)^2+(y-2)^2=4}[/tex]
Quite frankly, I don't see any circle below.
But the equation of the circle that you've described is . . .
(x - 1)² + (y - 2)² = 4 .
