Question

How many terms of the ap 27, 24, 21, …should be taken so that their sum is 0?

Answer 1

in the given ap a=27,d=-3
and we have to find 'n' when Sn=0
Sn=n/2(2a+(n-1)d)
therefore 0=n/2(54+(n-1)(-3))
0=n(54-3n+3)
0=54n-3n^2
therefore n=19 ans


thanks