Solution
= Solution
Since $z\bar z=x^2+y^2$, the real <quadratic equation> is
$$
x^2+y^2+2b_1x+2b_2y+c=0.
$$
<Completing the square> makes its geometry explicit:
$$
\boxed{(x+b_1)^2+(y+b_2)^2=b_1^2+b_2^2-c}.
$$
= Solution
Since $z\bar z=x^2+y^2$, the real <quadratic equation> is
$$
x^2+y^2+2b_1x+2b_2y+c=0.
$$
<Completing the square> makes its geometry explicit:
$$
\boxed{(x+b_1)^2+(y+b_2)^2=b_1^2+b_2^2-c}.
$$