$\displaystyle\frac{{{{b}}^{{2}}-{1}}}{{{{b}}^{{2}}+{1}}}\usepackage{cmbright}\Huge\$ ; domain is all $\displaystyle{b}\usepackage{cmbright}\Huge\$ , $\displaystyle{b}\ne{0}\usepackage{cmbright}\Huge\$ , 1, and -1