Question

Find the sum of the first 25 terms of an A.P. whose nth term is given by a_n = 7 − 3n.

Answer 1

Here, we are given an A.P. whose n^th term is given by the following expression, . We need to find the sum of first 25 terms.

So, here we can find the sum of the n terms of the given A.P., using the formula,

Where, a = the first term

l = the last term

So, for the given A.P,

The first term (a) will be calculated using in the given equation for n^th term of A.P.

Now, the last term (l) or the n^th term is given

So, on substituting the values in the formula for the sum of n terms of an A.P., we get,

Therefore, the sum of the 25 terms of the given A.P. is.