/sci/ - Science & Math

Can someone give me hints on how to do this?
I know that I would eventually have to put the expression into -1<r<1
What I'm thinking of is:
1) Split (-1/7)^n and (x-8)^n to their own series and do them individually.
2) (-1/7)^n would just be geometric series
3) (x-8) would be plugged into -1<r<1
Is my 'plan' correct? I don't actually know if it's allowed to do (1)

Can someone give me hints on how to do this?
I know that I would eventually have to put the expression into an equality.
What I'm thinking of is:
1) Split (-1/7)^n and (x-8)^n to their own sequences and do them individually.
2) (-1/7)^n would just be geometric series
3) (x-8)^n would be plugged into the an inequality.
Is my 'plan' correct? I don't actually know if it's allowed to do (1)