a+8d = 23
a+32d = -241
subtract them ...
24d = -264
d = -11
back into the first ....
a - 88 = 23
a = 111
now that we know a = 111, d = -11 and n = 15
just plug those values into your formula
the ninth term of an arithmetic sequence is 23 and the 33rd term of the sequence is -241 , calculate the sume of the first 15 terms of the sequence , using the formula
s=n(2a+(n-1)d)/2
3 answers
Sn=510
S15 =510
1 answer