Question

The first term of an arithmetic sequence is 5 and the common difference is 2. Find the sum of its first 25 terms.

Answer 1

First term of an arithmetic sequence = a + b = 5

Common difference = a = 2

⇒ 2 + b = 5

⇒ b = 5 − 2 = 3

Therefore, n^th term of the given arithmetic sequence is

We know that the sum of a specified number of the consecutive terms of an arithmetic sequence is half the product of the number of the terms with the sum of the first and the last term.

∴ Sum of its first 25 terms = … (1)

Here,

Putting the values in equation (1):

Sum of first 25 terms =