I need help on number three pls help

Answer:
(1/2)n
Step-by-step explanation:
I think this should be correct. A will be "1" and then for every scale (n) it will be scaled by 1/2.
Have a nice day!
I hope this is what you are looking for, but if not - comment! I will edit and update my answer accordingly. (ノ^∇^)
- Heather