Answer:
Step by step solution:
This is an arithmetic sequence a, a+d, a+2d, a+3d, ..., where a is the initial term and d the common difference.
For 21, 16, 11, 6, ....
The initial term a = 21 and the common difference is d = 5, then the next 3 terms are
21, 16, 11, 6, 1, -4, -9. This representation is explicit
