Let Sn= 12+ 16+ 112+ 120+ upto n terms. If the sum of the first six terms of an A.P. with first term -p and common difference p is 2026 S2025, then the absolute difference between 20th and 15th terms of the A.P. is
- 20
- 45
- 90
- 25
Answer
(4) 25
Solution
Sn= ( 1k- 1k+1 )= nn+1 2026 S2025= 2025=45
A.P. a=-p, d=p: S6=3 [-2p+5p ]=9p=45 p=5
|T20-T15|=5d=5p=25
Answer: (4)