# geometric sequence help

• Jul 19th 2013, 07:42 AM
dzomberg
geometric sequence help
List the first four terms of a geometric sequence with t1 = 4 and tn = -3tn-1.
How do I find r???
• Jul 19th 2013, 08:05 AM
Plato
Re: geometric sequence help
Quote:

Originally Posted by dzomberg
List the first four terms of a geometric sequence with $\displaystyle t_1 = 4$ and $\displaystyle t_n = -3t_{n-1}$.
How do I find r???

Well $\displaystyle t_2=-3(t_1)$. Now you post what you get!
• Jul 19th 2013, 08:05 AM
Soroban
Re: geometric sequence help
Hello, dzomberg!

Quote:

List the first four terms of a geometric sequence with:- $\displaystyle t_1 = 4\,\text{ and }t_n = \text{-}3\!\cdot\!t_{n-1}$

How do I find $\displaystyle r$?

Just read what you are given . . . and crank out the list.

$\displaystyle t_1 = 4$ . . . The first term is 4.

$\displaystyle t_n = \text{-}3\!\cdot\!t_{n-1}$ . . . Each term is -3 times the preceding term.

Therefore:

. . $\displaystyle \begin{array}{cccccc}t_1 &=& 4 &=& \;4\\ t_2 &=& \text{-}3(4) &=& \text{-}12 \\ t_3 &=& \text{-}3(\text{-}12) &=& \;36 \\ t_4 &=& \text{-}3(36) &=& \text{-}108 \end{array}$
• Jul 19th 2013, 10:05 AM
topsquark
Re: geometric sequence help
Quote:

Originally Posted by dzomberg
List the first four terms of a geometric sequence with t1 = 4 and tn = -3tn-1.
How do I find r???

....And please learn to use LaTeX (as in our LaTeX help forum) or learn how to use parenthesis. tn = -3t(n-1) is a bit better anyway. t_n = -3t_(n - 1) would be best.

-Dan