9. The first two terms of an arithmetic series are \(( t - 1 )\) and \(\left( t ^ { 2 } - 5 \right)\) respectively, where \(t\) is a positive constant.
- Find and simplify expressions in terms of \(t\) for
- the common difference of the series,
- the third term of the series.
Given also that the third term of the series is 19 ,
- find the value of \(t\),
- show that the 10th term of the series is 75,
- find the sum of the first 40 terms of the series.