11. The first term of an arithmetic sequence is 30 and the common difference is - 1.5
- Find the value of the 25th term.
The \(r\) th term of the sequence is 0 .
- Find the value of \(r\).
The sum of the first \(n\) terms of the sequence is \(S _ { n }\).
- Find the largest positive value of \(S _ { n }\).