#18,19 Help ​

18.

Since  each successive term  is greater than the previous term.....this series will diverge and will not have a definite sum.......another way to see this is that the common ratio  is 3......for a series to converge, r  must have an absolute value < 1

19.

a)     a₁  = 9,    a_n  = a_n-1 + 2

b)   a_n  =  9  + 2 (n - 1)

c)  a₁₂  =  9 + 2(12 - 1)   =   9 + 2*11  =  9 + 22   =   31 seats