Awnswer:
[tex]9a^2-6a-7[/tex]
Stewp-by-stewp exwplanation:
[tex]\left(7a^2+3a-6\right)+\left(2a^2-9a-1\right)[/tex]
[tex]=7a^2+3a-6+2a^2-9a-1[/tex]
[tex]=7a^2+2a^2+3a-9a-6-1[/tex]
[tex]=9a^2+3a-9a-6-1[/tex]
[tex]=9a^2-6a-6-1[/tex]
[tex]=9a^2-6a-7[/tex]
