Question

Whats the equation for a question as following:
"What is the 20th term of the arithmetic sequence 4, –2, –8, "

Answer 1

This site might be helpful: http://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html

Answer 2

hmmmm @asnaseer could you help me with the question above then.
I get that xn=a+d(n-1) but Im not sure how to plug stuff in:/

Answer 3

in the equation you just posted, we have:\[x_n=a+d(n-1)\]have your read that web page to understand what each of these symbols stand for?

Answer 4

for example, what does the "a" stand for?

Answer 5

a=first term. So in this case "4."

Answer 6

correct - what about the other symbols?

d = ?
n = ?

Answer 7

d=-6
n=?

Answer 8

do you know what "n" stands for?

Answer 9

...its the term right? So 20?

Answer 10

perfect! :)

yes, "n" stands for the n'th term - in your case you want the 20'th term so (as you said) n=20

Answer 11

so use the formula to wok out \(x_{20}\)

Answer 12

S0 x20= 4+ -6(19)?
x20=4-114
x20=-110?:)

Answer 13

perfect again!

you have the right answer. :)

Answer 14

Ha Thanks! Last thing, so I don't start a whole new questions:
"What is the sum of a 38–term arithmetic sequence where the first term is 14 and the last term is 154?"
whats d?:/

Answer 15

The code of conduct for this site states that you should post each question separately.

This also helps others learn by them being able to see your question and delving in if they are interested.

Answer 16

I'll help you once you have posted it. :)