Question

What is the general term equation, an, for the arithmetic sequence 9, 5, 1, −3, . . . , and what is the 21st term of this sequence?

Answer 1

Can you see what the pattern is?

Answer 2

As in, firstly, can you describe the pattern which the arithmetic sequence follows?

Answer 3

Hint: an = a1 + d(n − 1), where a1 is the first term and d is the common difference.

Answer 4

@chris5122 than you see it 5 is smaler than 9 by 4 - yes ?
and so the other 1 is smaler than 6 by 4 - yes ?
so how you think it ?

Answer 5

sorry for my mistake so 1 is smaler than 5 by 4

Answer 6

yes

Answer 7

so than what will be the 21th term ?

Answer 8

Thats what im asking help with..

Answer 9

You're looking for the "common difference." From one term to the next, you see a decrease. How much is this decrease? Call it " d ." This is the "d"
to which Chris is referring in : an = a1 + d(n − 1)

Answer 10

Im really just looking for the 21st term

Answer 11

Excuse me for saying so, Chris, but you're completely missing the point. To use the formula an = a1 + d(n − 1), you MUST know what "common difference" means and be able to find it. Were I to give you the 21st term, you'd learn next to nothing .

Answer 12

What is the common difference? What is the jump / leap from 9 to 5, from 5 to 1, etc.?

Answer 13

ohhhhh

Answer 14

the pattern

Answer 15

Yes, the pattern. ??

Answer 16

so -4

Answer 17

Yes, the "common difference" is d = -4. So much better.

Now, write out that formula, replacing "d" with -4. an = a1 + d(n − 1)

Answer 18

I think i may know it

Answer 19

would it be an=9-4n, a21=-75

Answer 20

the first term is 9. Call this "a1" ("a sub 1"). d = -4. To find the 21st term, subst. 21 for n in the equation.

Answer 21

Please show how you got -75. Note that a1=9, d=-4, and n=21.

Answer 22

one second im doing the work

Answer 23

Excuse me, but where are you?

Answer 24

Here

Answer 25

Im sorry

Answer 26

Your work, please?

Answer 27

well since 9 was the first term i could figure out by process of elimination what the answer was. There is only one answer where the first term is 9.

Answer 28

Its a multiple choice question so since a1=9 that gave me the answer.

Answer 29

why not learn how to do this problem properly? Please use the equation\[l=a + (n-1)d\] where a= first term, d=common difference, n=the index of the term wanted, and l=last term.

You 'll need to calculate the last (the 21st) term, d.

Answer 30

a=?

d=?

n=?

l=?

Answer 31

Well better off doing it the right way..

Answer 32

one second ill answer it

Answer 33

I get confused when you say index of the term wanted?

Answer 34

what do you mean by that?

Answer 35

n is a counter, like your fingers are counters when you count 1, 2, 3, ...

First term could be

Answer 36

2nd term could be