cooldudeachyut
New member
- Joined
- Nov 6, 2015
- Messages
- 18
Question : Find the sum of the series - 12 - 22 + 32 - 42 + 52 ...... n terms
My attempt : I took two terms of the series as (2k-1)2 - (2k)2 = 1-4k
So adding the series as ∑(1-4k) taking range of k from 1 to n/2 (since I'm taking two terms at the same time), I got the answer :- -n(n+1)/2
but my textbook has given the answer as :- -n(2n+1)
Please help.
My attempt : I took two terms of the series as (2k-1)2 - (2k)2 = 1-4k
So adding the series as ∑(1-4k) taking range of k from 1 to n/2 (since I'm taking two terms at the same time), I got the answer :- -n(n+1)/2
but my textbook has given the answer as :- -n(2n+1)
Please help.