[tex]9( {a}^{2} + 1) {}^{2} - 4( {b}^{2} - 1) {}^{2} [/tex]
[tex] = 9( {a}^{4} + 1) - 4( {b}^{4} + 1)[/tex]
[tex] = {9a}^{4} + 9 - {4b}^{4} - 4[/tex]
[tex] = {9a}^{4} - {4b}^{4} + (9 - 4)[/tex]
[tex] = {9a}^{4} - {4b}^{4} + 5[/tex]
