An arithmetic sequence a begins 11, 7, ...

1.  a_n  = a_n-1  - 4,  a₁  = 11 

2. Here :  https://www.desmos.com/calculator/xnzwqsnu8u

3. Probably wouldn't want to use the recursive formula to find the 100th term......we would have to find the first 99 terms and then subtract 4 from the 99th term.....extremely tedious....!!!