arithmetic
posted by jae .
Find the sum of the first 25 terms of an arithmetic sequence whose 7th term is −247 and whose 18th term is −49.

7th term = 247 > a+6d = 247
18th term = 49 > a+17d =49
subtract them:
11d = 198
d = 18
in a+6d = 247
a + 108 = 247
a = 355
sum(25) = (25/2)(710 + 24(18)) = 3475 
Db

Gw scc ucjdnwgdj I've k
Dha ex jkv
Dfjcjmejm
Defied
Defieddjcjm
Cjnmd
D j
Ex nm
Dj
Fujsiqix
Click
Scc u hm dc
Dc m
D
From
F
Fjcjdjcjcnfjc
Djjpsdodjdii
Jm
F
F
Dujfjd
Dcjnd
Fjnmf
Find
Mdmjf
Mum
Ffjmmj
Jdjj
Jdf
Did
Didn't
Jdjcjdncjm
Did
Jdjcjdncjm