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 \displaystyle \left( a \right.,\left. b \right) and radius \displaystyle r,

\displaystyle \left( x-a \right)^{2}+\left( y-b \right)^{2}=r^{2}

In our case, we can write the equation as

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

and then we see that it describes a circle with centre at \displaystyle \left( 1 \right.,\left. 2 \right) and radius