Question

How do you graph y = ax^2 - 6ax + (9a + 8)

Answer 1

You don't. A value for 'a' is required. Alternatively, you can select various values for 'a' and show a "family" of curves.

Answer 2

a is -4<a<4

Answer 3

There you go. Try a=4 and a=-4 and a=0 and see if you should look closer. In particular, a = 0 is very interesting.