From Förberedande kurs i matematik 1

A quick way to interpret the equation is to compare it with the standard formula for the equation of a circle with centre at (a,b) and radius r,

\displaystyle (x-a)^2 + (y-b)^2 = r^2\,\textrm{.}

In our case, we can write the equation as

\displaystyle (x-1)^2 + (y-2)^2 = (\sqrt{3})^2

and then we see that it describes a circle with centre at (1,2) and radius \displaystyle \sqrt{3}\,.