Questions regarding further (number patterns)

[philmurray58]

1. Why sometimes is the correct formula for working out a sequence
Tn=5x26(n-1) and sometimes its just Tn=5x2^n
I'm really confused

2. How to enter a difference equation into a calculator which has a geometric ratio and an arithmetic change such as
Dn= 1.4D n-1  - 10 D0= 32

thanks guys

[kamil9876]

1.) That depends on the sequence really. if you want: {5,10,20,40...} then you would use the first, whereas if you wnt {10,20,40...} you use the latter. I guess in practical applications, if it said "started off with 5$ on day 1 and his money doubles each day, how much does he have on day n?" would involve the first sequence, hence first formula. Whereas if "he starts of with 5$ on day 1 at 9am and it doubles everyday at noon, how much does have at 1pm on day n?" would involve the second sequence, hence second formula.

[Harbourmastah]

yes it depends on the whether the first number they give you is the first number of the sequence i.e. t1 or the initial number, i.e. t0

i've seen many practice exams mess this on up >.>