1/3(9ab的2次方-3)+(7a的2次方b-2)+2(ab的2次方+1)-2a的2次方b
=(3ab^2-1)+7a^2b-2+2ab^2+2-2a^2b
=3ab^2+2ab^2+7a^2b-2a^2b-2+2
=5ab^2+5a^2b
=5ab(a+b)