Asked by rose

The sum of the first 15 terms of an arithmetic series is 1290. The sum of the first 16 terms is 1464.
Find t16? Find S20
Answered by Steve
clearly T16 = 1464-1290 = 174

16/2 (a+174) = 1464
a = 9

T16 = 9+15d = 174
d=11

S20 = 20/2 (2*9+11*19) = 2270