The complex conjugate of $\displaystyle{a}+{b}{i}\usepackage{cmbright}\Huge\$ is $\displaystyle{a}-{b}{i}\usepackage{cmbright}\Huge\$ . Therefore the complex conjugate of $\displaystyle{5}-{i}\usepackage{cmbright}\Huge\$ is $\displaystyle{5}+{i}\usepackage{cmbright}\Huge\$ .