Can someone do this assuming that it is infinite and as well as assuming it's not infinite? Thanks!

see below

Step-by-step explanation:

4,7,12,19

We are adding 3,5,7,9..... each time

The sequence is not arithmetic because we are not adding a constant.  It is not geometric since we are not multiplying by a constant term each time

There is no common difference  or common ratio.

The explicit formula is

an =n^2 +3

The recursive formula is

(n+1)^2 +3 - (n^2 +3)

    n^2 +2n+1+3 - ( n^2+3)

      2n+1

a sub(n+1) = a sub( n) + 2n+1

The 10th term

an      = n^2 +3

Let n=10

an = 10^2+3

    = 100+3

    = 103

summation

see image

since the numbers are increasing and greater than 1 the sum does not exist