Find the sum of the first 25 terms of an A.P. whose nth term is given by .
Given, an= 7 - 3n
Put n = 1
a1= 7 – 3(1) = 4
Put n = 25
a25= 7 – 3(25) = -68 = l
S25= [4 – 68]
= 25 [-32] = -800