Find the sum of the first n terms of an arithmetic sequence.

The sum of the first n terms of an arithmetic sequence is given by Sn = n/2(2a + (n-1)d).

An arithmetic sequence is a sequence of numbers where each term is obtained by adding a fixed number (called the common difference) to the previous term. For example, 2, 5, 8, 11, 14 is an arithmetic sequence with a common difference of 3.

To find the sum of the first n terms of an arithmetic sequence, we use the formula Sn = n/2(2a + (n-1)d), where a is the first term, d is the common difference, and n is the number of terms.

Let's take the example of the arithmetic sequence 2, 5, 8, 11, 14. Here, a = 2, d = 3, and n = 5. Substituting these values in the formula, we get:

Sn = 5/2(2(2) + (5-1)3)
= 5/2(4 + 12)
= 5/2(16)
= 40

Therefore, the sum of the first 5 terms of the arithmetic sequence 2, 5, 8, 11, 14 is 40.

It is important to note that the formula for the sum of an arithmetic sequence only works if the sequence is finite (i.e. has a last term). If the sequence is infinite, the sum is undefined.