\\z^2=a+ib\\|z^2|=|a+ib|\\|z|^2=|a+ib|\\(\sqrt{x^2+y^2})^2=\sqrt{a^2+b^2}\\x^2+y^2=\sqrt{a^2+b^2} \ (*)\\$Now, $\\(x+iy)^2=a+ib\\(x^2-y^2)+2ixy=a+ib\\$Equating $\Re (z),\\x^2-y^2=a\Rightarrow y^2=x^2-a \ (**)\\$Sub $(**) $ in $(*),\\2x^2=a+\sqrt{a^2+b^2}
edit: beaten by the Treb Man