anonymous one year ago Find an explicit rule for the nth term of a geometric sequence where the second and fifth terms are -36 and 2304, respectively.

1. anonymous

do you have a general idea?

2. anonymous

i tried using this http://openstudy.com/study#/updates/513cdcd0e4b029b0182b5689 and i did -36 - ar 2304 = ar^4 2304 = ar * r^3 2304 = -36 * r^3 2304 = r^3????????

3. anonymous

with r being the common ratio but i didn't get an integer

4. zepdrix

your second to last step looks correct 2304 = -36 * r^3 what happened to the -36 in the next step? did you mean to divide the 2304 by that amount?

5. anonymous

r^3=2304/-36=?

6. anonymous

-64

7. anonymous

$r^3=\left( ? \right)^3$ r=?

8. anonymous

cube root it = 4?

9. anonymous

no

10. anonymous

4^3=64

11. anonymous

$r^3=-64=\left( -4 \right)^3,r=-4$

12. anonymous

does that mean it would be an = 9 * (-4)^n - 1?

13. anonymous

correct.

14. anonymous

YAY thanks :)))

15. anonymous

yw