Find the vertex of the function if x=1

options:
(1,24)
(1,30)
(1,32)
(1,41)

Asocial networking site currently has 400,000 active members, and that figure is predicted to increase by 32% each year. the following expression represents the number of active members on the site after t years.

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Solve: 25 points find the fifth term of an increasing geometric progression if the first term is equal to 7−3 √5 and each term (starting with the second) is equal to the difference of the term following it and the term preceding it.