Math (precalculus)
posted by Angellove on .
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=3an1 1.
(It's: a sub 1 =2, a sub n= 3a sub n1 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!)

asub1 = 2 is the first term
asubn can be calculated fron asubn1, using the formula you prodided
asubn = 3 asubn1 1
Thus a sub2 = 3 asub1  1 = 5
asub3 = 3 asub2 1 = 14
asub4 = 3 asub3 1 = 41
asub5 = ? 
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!

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! 
Looks good to me!
It's interestng that the differences between adjacent terms are powers of 3:
3,9,27,81 etc 
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?