Question

Which expression defines the given series for seven terms?

15 + 19 + 23 + . . .

Answer 1

hmm.. have you checked for a common difference?

Answer 2

arithmetic sequence looks like the following,
\[a_1,a_1+1d,a_1+2d,a_1+3d, \cdots, a_1+(n-1)d \\ \text{ where the } n^{th} \text{ term is } a_1+(n-1)d \\ \text{ which is usually denoted } a_n \\ \text{ so } a_n=a_1+(n-1)d\]

Answer 3

\[\sum_{0}^{6}(15+4n)\]

Answer 4

where \[a_{n}=15+4n\]