Answer:
[tex]12a^2-9a+5[/tex]
Step-by-step explanation:
We are required to evaluate:
[tex](5a^2-6a-4)-(-7a^2+3a-9)[/tex]
First, we open the bracket
[tex]=5a^2-6a-4+7a^2-3a+9[/tex]
Next collect like terms
[tex]=5a^2+7a^2-6a-3a+9-4[/tex]
Simplify your result
[tex]=12a^2-9a+5[/tex]