## anonymous one year ago Will medal and fan What is the sum of the geometric sequence -4, 24, -144 . . . if there are 6 terms? -159,963 26,660 26,661 159,963

1. anonymous

do 144 times neg 6 and that times neg 6 and that again times neg 6 to get all 6 terms

2. anonymous

3. anonymous

I did and the answer I got isn't the same as the options

4. xapproachesinfinity

you mean the sum of geometric series not sequence?

5. anonymous

No it says sequence

6. xapproachesinfinity

first you need to find all the 6 terms then sum up

7. xapproachesinfinity

you have three terms so you are missing three more to make 6 terms

8. xapproachesinfinity

what is the fourth term?

9. anonymous

864, -5184, 31104 thee are the next three terms. At least that's what I got. If I add them up I don't get one of the answers they provide

10. xapproachesinfinity

hmm really then you must of made a mistake

11. xapproachesinfinity

how did you get the fourth term for example

12. anonymous

$-144 \times -6 = 864$

13. xapproachesinfinity

yes!

14. xapproachesinfinity

you should get the right answer i don't where you missed

15. xapproachesinfinity

let's try doing the fomula $S_n=\frac{a(1-r^n)}{(1-r)}$

16. xapproachesinfinity

a=first term n=6 r=-6

17. xapproachesinfinity

@Tarynrachelle where you going?

18. anonymous

I'm still here I'm doing the problem

19. xapproachesinfinity

well low and behold i get one of the answer choices

20. xapproachesinfinity

you should get the right answer once you do the calculations

21. anonymous

22. xapproachesinfinity

and actually i get the correct answer even the method i told you in the start without formula. all of them should work since the formula came from it to begin with

23. xapproachesinfinity

no

24. anonymous

Idk what I'm doing wrong then.

25. xapproachesinfinity

well to me they all give the same answer, something must be wrong in yur work

26. xapproachesinfinity

anyway you got the formula, you got the other way just see where you had missed things

27. xapproachesinfinity

did you do it yet?

28. xapproachesinfinity

use the formula

29. anonymous

Okay well this is what I plug into the formula$S _{n}=\frac{ 4(1-(-6)^{6}) }{ (1-(-6)) }$ am I wrong?

30. xapproachesinfinity

yeah

31. anonymous

That's supposed to be a -4

32. xapproachesinfinity

yes -4 not 4 just about to say that

33. anonymous

Is it still wrong even with the -4? Or is it correct with the -4?

34. xapproachesinfinity

it is correct with -4

35. anonymous

Okay. Hold on I think I see where I messed up

36. anonymous

Nope still not getting one of the answer choices..

37. anonymous

I plug it into my calculator and get 186614. That's the same answer I get when I add them all up

38. anonymous

Could you explain the steps for me so I know what I'm doing wrong?

39. xapproachesinfinity

hold a sec

40. xapproachesinfinity

ok back

41. xapproachesinfinity

how did you put it in your calc?

42. anonymous

$-4(1-(6)^6)\div(1-(6))$

43. xapproachesinfinity

no bottom is (1-(-6))=1+6

44. xapproachesinfinity

where are the negatives of 6?

45. anonymous

My calculator wasn't getting the right answer but this is it http://www.wolframalpha.com/input/?i=-4%281-%28-6%29%5E6%29%2F%281-%28-6%29%29

46. xapproachesinfinity

well for the top you didn;t have to worry a lot of that negative since you have an even power but bottom no

47. anonymous

It's the second choice

48. xapproachesinfinity

yes!

49. xapproachesinfinity

i think you put the wrong format into your calc

50. anonymous

Probably. But thank you

51. xapproachesinfinity

No problem