# how to determine the general term

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• April 8th 2010, 10:40 AM
needhelpplease1
how to determine the general term
#1: Determine the general term, tn, for sequence/series 64, -16, 4, -1,...

I have no idea how to do this :(
• April 8th 2010, 10:53 AM
mathemagister
Quote:

Originally Posted by needhelpplease1
#1: Determine the general term, tn, for sequence/series 64, -16, 4, -1,...

I have no idea how to do this :(

Here's a clue: notice how each term is -1/4 times the previous term. This, and your notes, should help you find the answer.
• April 8th 2010, 10:54 AM
harish21
Quote:

Originally Posted by needhelpplease1
#1: Determine the general term, tn, for sequence/series 64, -16, 4, -1,...

I have no idea how to do this :(

$a_{n+1} = \frac{-a_n}{4}$

Note: This is the recurrence relation.

The series is expressed as what mathemagister has stated:

${a_n} = [-(-1)^n] 4^{4-n}$
• April 8th 2010, 10:58 AM
mathemagister
And that translates to $a_n = -(-1)^n 4^{4-n}$
• April 8th 2010, 11:07 AM
needhelpplease1
hmm..
Quote:

Originally Posted by mathemagister
And that translates to $a_n = -(-1)^n 4^{4-n}$

wait, wouldn't it be $tn = 64(-1/4)^n$?
• April 8th 2010, 11:11 AM
mathemagister
Quote:

Originally Posted by needhelpplease1
wait, wouldn't it be $tn = 64(-1/4)^n$?

No, because then when n = 1, you wouldn't get 64.

EDIT: I think you were thinking of $t_n = 64(-1/4)^{n-1}$ which is also a correct way to express the sequence.

Hope everything is clarified :)

Mathemagister