Question

the sum of the first ten terms of a linear sequence is -60 and the sum of the first fifteen of the sequence is -165 find the 18th term of the sequence?

Answer 1

(10/2)(2a + 9d) = -60
2a + 9d = -12

(15/2)(2a + 14d) = -165
2a + 14d = -22
subtract them: 5d = -10 ---> d = -2
in 2a + 9d = -12
2a - 18 = -12
a = 3

now that you know that a=3 and d=-2
find term(18) = a + 17d = .....

Answer 2

-31

Answer 3

i dont understand

Answer 4

i dont understand the question

Answer 5

please use another method