What is the formula for finding tn in a sequence or series?

[Nelo]

Homework Statement

I wrote a test and the question was something like this

2, 4, 6... 108

It said... " Find tn"

Does this just mean find any term number that isn't given? I just plugged in t5 for the arithamtic logic and solved.. don't know if it was right, does anyone know?

Homework Equations

The Attempt at a Solution

 

[Nelo]

Bump for someone giving a one word answer like "yes" or "no" based on what i presented

 

[ArcanaNoir]

It's hard to understand from what you wrote, but I think the answer they were going for was "2n".

 

[Nelo]

How is that hard to understand...


>given series

> 2, 4, 6... 108

> Solve tn

Thats all it said. So i just solved any random term. In the book it usually gave a term like solve for t4 . But this time it didnt.

Does it just mean solve for an unknown.

 

[ArcanaNoir]

Then it means solve for the nth term. The answer is 2n.

 

[PeterO]

Homework Statement

I wrote a test and the question was something like this

2, 4, 6... 108

It said... " Find tn"

Does this just mean find any term number that isn't given? I just plugged in t5 for the arithamtic logic and solved.. don't know if it was right, does anyone know?

Homework Equations

The Attempt at a Solution

The book said find tn, why did you chose t5?

I think you probably have a couple of formulae for tn, in terms of the first term [sometimes called "t1", sometimes called "a"] along with either the common difference [d] or the common ratio [r] depending whether it is an arithmetic or geometric sequence.

You were required to recognise which sequence this one is, identify the first term and common difference or ratio then substitute in the general formula to get a specific expression for tn.
Once you have that, t4 is what you get when you replace n with 4.

I suspect you have worked with the answer, without realising it was the answer.

 

[Nelo]

Yes, I've worked with the answer. I jus realsied its the same thing as when they give you two terms.

ie) t1= 2
t2 = 4 ... Then ask you to find tn.

Finding tn, meaning getting the equation for both points then using elimination and solving for d and a , etc.

6 marks lost for no reason woo^^

 

[PeterO]

Yes, I've worked with the answer. I jus realsied its the same thing as when they give you two terms.

ie) t1= 2
t2 = 4 ... Then ask you to find tn.

Finding tn, meaning getting the equation for both points then using elimination and solving for d and a , etc.

6 marks lost for no reason woo^^

Might I suggest that when preparing for an exercise on Sequences & Series, you prepare your self a list of things to find BEFORE reading the question. Reading the question will only distract you!

That list would include:

First term, Common Difference or Common Ratio, Formula/expression for the nth term, the value of a specific term, formula/expression for the Sum of a group of terms, etc...

You then read the question to see which one or more of those things they asked you for this time.