Hallo,
\( \frac{1+z^{2}}{z}=0,001=\frac{1}{1000} |* z \)
\( 1+z^{2}=\frac{1}{1000} z \quad |-\frac{z}{1000} \)
\( z^{2}-\frac{1}{1000} z+1=0 \quad p q- \) Formel
\( z_{1 / 2}=\frac{1}{2000} \pm \sqrt{\frac{1}{4000000}-1} \)
\( z_{1 / 2}=\frac{1}{2000} \pm i \frac{\sqrt{3999999}}{2000} \)