if the 8th term of an AP is 37 and the 5th term is 15 more than the 12th term. find the AP. hence find the sum of the first 15 terms of the AP.

Answer 1

a+7d = 37
a+4d - (a+11d) = 15
-5d = 15
d = -3

into the first:
a - 21 = 37
a = 58

sum(15) = (15/2)(116 + 14(-3))
= 555