Question

fin the sum of all even integers between 21 and 135

Answer 1

For an arithmetic sequence with first term a, common difference d, and number of terms n, the sum is

\(S = \dfrac{2a + (n - 1)d}{2} \)

Answer 2

Also, the formula for the nth term is:

\(a_n = a_1 + (n - 1)d\)

You know the first term is 22, and the last term is 134.

Use this first to find n, the number of terms.