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


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