Solution
= Solution
\b[No finite choice of $b$ and $c$ gives a line.] The coefficient of $zz^*=x^2+y^2$ is fixed at one, so completing the square always gives a <circle>, a point, or the empty set. A general equation $Azz^*+bz^*+b^*z+c=0$ could describe a line when $A=0$ and $b\ne0$, but changing the fixed quadratic coefficient is not permitted here. A limiting sequence of increasingly large <circles> does not make any one of these finite equations a line.