-(a²-2ab)×9a²-(9ab³+12a^4b²)÷3ab=

-(a²-2ab)×9a²-(9ab³+12a^4b²)÷3ab=

-(a²-2ab)×9a²-(9ab³+12a^4b²)÷3ab
=-9a^4+18a³b-3b²-4a³b
=-9a^4+14a³b-3b²

-(a²-2ab)×9a²-(9ab³+12a^4b²)÷3ab
=-9a^4+18a^3b-3b^2-4a^3b
=-9a^4+14a^3b-3b^2