# Homework Help: Geomtric sequence agghh!

1. Sep 9, 2008

### hostergaard

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.

2. Sep 9, 2008

### praharmitra

you can find tn by

$$u_{n} = s_{n} - s_{n-1}$$

Then find $$u_{m}$$ by applying properties of geometric sequence. work back and find m

3. Sep 11, 2008

### HallsofIvy

In particular, $$u_2= s_2- s_1$$. Find $$s_2$$ and $$s_1$$ from the formula you are given and subtract. $$u_{32}= s_{32}- s_{31}$$. Again find those and subtract. Now you know two terms of a geometric sequence you can find the term between them. $$\frac{u_m}{u_2}= \frac{u_{32}}{u_m}$$.

Last edited by a moderator: Sep 11, 2008
4. Sep 11, 2008

### Diffy

Helpiamtrappedinatextagandican'tescapefromit!