− z 2 a 6 − 2 a 6 + z 4 a 4 + 4 z 2 a 4 + 3 a 4 {\displaystyle -z^{2}a^{6}-2a^{6}+z^{4}a^{4}+4z^{2}a^{4}+3a^{4}}
