Posted by **Angellove** on Sunday, November 2, 2008 at 12:57pm.

Hi! I have a question! I forgot how to do these two problems, and I need some help in solving them! Thanks so much!

1.) Find the first 5 terms of the sequence given by a1=2, an=3an-1 -1.

(It's: a sub 1 =2, a sub n= 3a sub n-1 -1)

Does that make sense?

If not, that's ok. I'll to clarify more if it's still strange (which it is, I know!)

- Math (pre-calculus) -
**drwls**, Sunday, November 2, 2008 at 1:26pm
asub1 = 2 is the first term

asubn can be calculated fron asubn-1, using the formula you prodided

asubn = 3 asubn-1 -1

Thus a sub2 = 3 asub1 - 1 = 5

asub3 = 3 asub2 -1 = 14

asub4 = 3 asub3 -1 = 41

asub5 = ?

- Math (pre-calculus) -
**Angellove**, Sunday, November 2, 2008 at 1:34pm
Okay!! I think I got it!!! Thank you so much! I'm gonna solve the 5 terms, and write them up here! :) Tell me how I did!

- Math (pre-calculus) -
**Angellove**, Sunday, November 2, 2008 at 1:37pm
Okay:

a sub1=2

a sub2= 3(2)-1=5

a sub3= 3(5)-1=14

a sub4= 3(14)-1=41

a sub5= 3(41)-1=122

I think that's it! Thanks so much again!

- Math (pre-calculus) -
**drwls**, Sunday, November 2, 2008 at 2:13pm
Looks good to me!

It's interestng that the differences between adjacent terms are powers of 3:

3,9,27,81 etc

- Math (pre-calculus) -
**adrienne **, Saturday, March 19, 2016 at 5:32pm
The monthly cost (in dollars) of water use is a linear function of the amount of water used (in hundreds of cubic feet, HCF). The cost for using 18 HCF of water is $33.44 , and the cost for using 35 HCF is $61.49. What is the cost for using 27 HCF of water?

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