If the sum of first p terms of an A.P. is equal to the sum of the first q terms, then find the sum of the first (p + q) terms.

Explanation

To solve the problem, we need to find the sum of the first (p + q) terms of an arithmetic progression (A.P.) given that the sum of the first p terms is equal to the sum of the first q terms.

### Step-by-Step Solution:

1. **Formula for the Sum of n Terms of an A.P.**:
The sum \( S_n \) of the first \( n \) terms of an A.P. can be expressed as:
\[
S_n = \frac{n}{2} \left(2a + (n - 1)d\right)
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