What is the value of m in the given geometric sequence?

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In summary, the given formula for the sum of the first n terms of an arithmetic sequence is sn=4n2-2n. Three terms of this sequence, u2, um, and u32, are consecutive terms in a geometric sequence. To find m, use the formula u_{n} = s_{n} - s_{n-1} to find u_{m} and then apply properties of geometric sequence to work backwards and find m.
  • #1
hostergaard
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the sum of the first n terms of an arithmetic sequence {un} is given by the
formula sn=4n2-2n. three terms of this secuence, u2 um and u32 are conscutive terms en a geomtric sequence. find m.

Yea, I am really confused... please help :-)
 
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  • #2
you can find tn by

[tex]u_{n} = s_{n} - s_{n-1}[/tex]

Then find [tex]u_{m}[/tex] by applying properties of geometric sequence. work back and find m
 
  • #3
In particular, [tex]u_2= s_2- s_1[/tex]. Find [tex]s_2[/tex] and [tex]s_1[/tex] from the formula you are given and subtract. [tex]u_{32}= s_{32}- s_{31}[/tex]. Again find those and subtract. Now you know two terms of a geometric sequence you can find the term between them. [tex]\frac{u_m}{u_2}= \frac{u_{32}}{u_m}[/tex].
 
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  • #4
Helpiamtrappedinatextagandican'tescapefromit!
 

1. What is a geometric sequence?

A geometric sequence is a sequence where each term is found by multiplying the previous term by a constant value called the common ratio. It follows the general formula an = a1 * rn-1, where a1 is the first term and r is the common ratio.

2. How do you find the common ratio in a geometric sequence?

The common ratio can be found by dividing any term in the sequence by the previous term. This will give you a constant value that is the common ratio for the entire sequence.

3. What is the difference between a geometric sequence and an arithmetic sequence?

In an arithmetic sequence, each term is found by adding a constant value to the previous term. In a geometric sequence, each term is found by multiplying the previous term by a constant value. This means that in a geometric sequence, the terms increase or decrease at an exponential rate, while in an arithmetic sequence, the terms increase or decrease at a constant rate.

4. What is the formula for finding the nth term in a geometric sequence?

The formula for finding the nth term in a geometric sequence is an = a1 * rn-1. This formula can be used to find any term in the sequence by plugging in the value of n and solving for an.

5. Can a geometric sequence have a negative common ratio?

Yes, a geometric sequence can have a negative common ratio. This means that the terms in the sequence will alternate between positive and negative values. For example, a geometric sequence with a common ratio of -2 would look like: 1, -2, 4, -8, 16, ...

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