Question

3. What is the sum of a 12-term arithmetic sequence where the last term is 13 and the common difference is -10?

Answer 1

Can you answer my question? This is not a public dating site. -_-

Answer 2

You need the first term of the sequence

an = a1 + d(n-1)

13 = a1 - 10(12-1)

13 = a1 - 10(11)

13 = a1 - 110

13+110 = a1

123 = a1

a1 = 123

So the first term is 123

Answer 3

With the first term, the last term and the number of terms, you can figure out what the first 12 terms add to

Answer 4

using this formula

S = (n*(a1 + an))/2

S = (12*(123 + 13))/2 ... plug in n = 12, a1 = 123 and an = 13

S = ??

Answer 5

karinewoods17, just ignore POOPSCOOPER153 since he looks like a troll to me

Answer 6

Thank you so much! I didn't know how to find the first term. You are so helpfull. I wish I could give you 1,000,000,000,000... medals:)

Answer 7

you're welcome

Answer 8

no not really, she's just grateful for me actually helping (instead of trolling)

Answer 9

Exactly! Ugh. stupid immature boys.

Answer 10

Is the answer 816?

Answer 11

you got it, the sum of the first 12 terms is 816

Answer 12

Thanks!

Answer 13

yw