Find the sum of first n terms of an AP whose nth term is 1 -4n. – InterviewSolution

1.

Find the sum of first n terms of an AP whose nth term is 1 -4n.

Answer»

Here it is given that, an= 1 - 4n

putting, n =1 , a1= 1- 4(1) = -3

putting, n =2 , a2= 1 - 4(2) = -7

Therefore, a = -3 and d = (-4)

Sn=n/2[2a+(n-1)d]Sn=n/2[-6+(n-1)(-4)]-3n-2n^2+2n

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