(﹣3a³)²·a³+(﹣4a)²·a的7次方+(﹣5a³)³
=9a^6·a³+16a²·a的7次方-125a^9
=9a^9+16a^9-125a^9
=-100a^9
(a+3b)(a²+9b²)(a-3b)
=(a+3b)(a-3b)(a²+9b²)
=(a²-9b²)(a²+9b²)
=a⁴-81b⁴