5n, -n, 7n...
2a-5, 2a+2, 2a+9...
I'm having trouble with the variables. Any problem solving help?
For the second, do you mean ? This would make the difference , the first initial term and thus you would be able to use the n'th term formula.
Are you sure about the first 3 terms of your first sequence? It would be nice if it were:
5n, -n, -7n
Then the common difference would be -6n. You simply add -6n four more times to get your four terms.
In the second one, 2a-5, 2a+2, 2a+9, you have a common difference of 7. Looks like each successive term is 7 more than the previous one. So, just add 7 four more times to get the next four terms.