If for an A.P. then
Explanation for the correct answer:
Step 1: Information required for the solution
To find the last term of an A.P, we use the formula,
where,
the nth term in the sequence
the first term in the sequence
the common difference between terms
Since which can be rewritten as
After further simplification we get,
Step 2: Calculation of the sum of the A.P
The formula used for the calculation of the sum of an A.P is
From the A.P, we know that , then
Hence, the correct option is (C).