Answer:
The answer is 9(a-2)(a+4).
Step-by-step explanation:
Use [tex]a^{2} -b^{2} =(a-b)(a+b)[/tex]
[tex]9(a+1)^{2} -81= 9( (a+1)^{2}-9)= 9( (a+1)^{2}-3^{2} )= 9(a+1-3)(a+1+3)\\=9(a-2)(a+4).[/tex]
