find the 20th term

Akarion · **Joined:** Fri, 6 Jan 2012 16:27:09 UTC **Posts:** 4

what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it

Shadow · **Posted:** Thu, 12 Jan 2012 22:22:35 UTC

Akarion wrote:

what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it

Are you given any other information? From what you have given us the next term could literally be ANYTHING. Do you know if the sequence is supposed to be arithmetic, for instance?

Akarion · **Joined:** Fri, 6 Jan 2012 16:27:09 UTC **Posts:** 4

the answers to choose from are 32,44,46 and yes arithmetic sequence

Denis · **Posted:** Fri, 13 Jan 2012 02:17:31 UTC

Are you too busy to do some work on this?
You could use google; you'd get sites like:
http://www.mathguide.com/lessons/Sequen ... metic.html

muckman · **Joined:** Fri, 13 Jan 2012 05:21:15 UTC **Posts:** 1

Shadow wrote:

Akarion wrote:

what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it

Are you given any other information? From what you have given us the next term could literally be ANYTHING. Do you know if the sequence is supposed to be arithmetic, for instance?

It's just sequential - should be 32.

Shadow · **Posted:** Fri, 13 Jan 2012 06:11:27 UTC

muckman wrote:

Shadow wrote:

Akarion wrote:

what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it

Are you given any other information? From what you have given us the next term could literally be ANYTHING. Do you know if the sequence is supposed to be arithmetic, for instance?

It's just sequential - should be 32.

Wrong, a sequence is not always arithmetic. And in support of my claim, I refer you to the Lagrange interpolation theroem.

simonsmith · **Joined:** Fri, 13 Jan 2012 06:35:41 UTC **Posts:** 2

the nth term formula is ---> (2n-8) where n is the term.

substitute 20 in the formula and you get 32.

Denis · **Posted:** Fri, 13 Jan 2012 07:42:00 UTC

simonsmith wrote:

the nth term formula is ---> (2n-8) where n is the term.

Why are you calling that a "formula"?

Shadow · **Posted:** Fri, 13 Jan 2012 07:45:40 UTC

Denis wrote:

simonsmith wrote:

the nth term formula is ---> (2n-8) where n is the term.

Why are you calling that a "formula"?

It is, of course, one of many possible formulas for that sequence, and if the op starts his sequences with n=1, and if the poster adds " a_n=

" and means to say that with the knowledge that it is supposed to be arithmetic.

kreshnik · **Joined:** Sun, 25 Dec 2011 00:28:25 UTC **Posts:** 95

Akarion wrote:

what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it

Hello,Akarion.

According to: $a_n=a_1+(n-1)d

if $a_1=-6\;\;\;\;,a_2=-4\;\;\;\;,a_3=-2\;\;\;\;\text{and}\;\;\;\;\;a_4=0$

$\text{we have:}$

$a_3=a_1+(3-1)d

$$d=\frac{4}{2}\;\;=>\;\;d=2$

So the difference is 2.

According to: $a_n=a_1+(n-1)d

$\text{We have:}$

$$a_{20}=-6+(20-1)2$

$$a_{20}=-6+19*2$

$$a_{20}=-6+38$

$$a_{20}=32$

like Shadow said:

Shadow wrote:

It is, of course, one of many possible formulas for that sequence, and if the op starts his sequences with n=1, and if the poster adds "a_n="

and means to say that with the knowledge that it is supposed to be arithmetic.

If it is arithmetic and if $a_1=-6

this is it. If is not ar. or anything else. Good Luck!

Denis · **Posted:** Fri, 13 Jan 2012 18:42:39 UTC

Well, Ma and Pa Kettle style, you're starting with -6, and by time you get to 20th,
you'll add 19*2 = 38; 38 - 6 = 32

Shadow · **Posted:** Fri, 13 Jan 2012 20:46:05 UTC

Denis wrote:

Well, Ma and Pa Kettle style, you're starting with -6, and by time you get to 20th,
you'll add 19*2 = 38; 38 - 6 = 32

Let's leave Ma and Pa out of this, if I recall they think that 25/5=14.

S.O.S. Mathematics CyberBoard

find the 20th term

Who is online