Question

Choose ONE of the following sequences and write​
the arithmetic or geometric EXPLICIT formula. Then use ​
your explicit formula to find the 18th term. (show all work)​
​
A) 3, 7, 11, 15,…...​
B) 2, 6, 18, 54,…...​
C) 6, 2, -2, -6,…...​

Answer 1

@darkknight 5 min l8r

Answer 2

?

Answer 3

ill get to u in 5 min.

Answer 4

oh, I need it right away my teacher needs the notes in 10 minutes and I still have a lot but it's okay :)

Answer 5

yea

Answer 6

nvm, i see it

Answer 7

ok

Answer 8

So which one do you want to choose? A B or C?

Answer 9

I think it b but I suck at math so idk

Answer 10

alright, lets work on B,
So we can see that B) 2, 6, 18, 54,…...​
the numbers are multiplied by 3 every time, starting at 2. So what do you think the arithmetic or geometric explicit formula will look like?

Answer 11

im not sure. I haven't worked a lot on arithmetic and geometric formulas

Answer 12

okay lets use the formula \[a _{n} = a _{1} + (n-1)d\]
this familiar to you?

Answer 13

not really but we can use it

Answer 14

It is basically saying that a n is equal to the 1st term + common difference (n-1)

Answer 15

okay

Answer 16

oops I got the wrong one. :(
So what i mean is that \[a _{n}= (a _{1}) (r)^(n-1)\]
Where r is the common ratio, in this case 3, a1 is initial value of in this case 2.
So we have an = 2 times 3^(n-1)

Answer 17

Sorry this is very messy, so basically \[a _{n} = 2(3)^(n-1)\]
N-1 is in the exponent btw

Answer 18

Okay thank you for your help so far

Answer 19

Now thats the formula, so plug in 18 for n and see what you get

Answer 20

No problem, If you want to drop a medal (best response) and have a good day :)