z 4 a 2 + z 4 − a 2 z 2 + 2 z 2 a 2 − z 2 a 4 + z 2 + 2 a 2 − 1 a 4 {\displaystyle {\frac {z^{4}}{a^{2}}}+z^{4}-a^{2}z^{2}+{\frac {2z^{2}}{a^{2}}}-{\frac {z^{2}}{a^{4}}}+z^{2}+{\frac {2}{a^{2}}}-{\frac {1}{a^{4}}}}
