*Help: Sequences and Series

E

edd fedds

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Joined
Dec 11, 2009
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*Need help on these question. I worked out the problems and wanted to check my solutions. I got a little confused on these. Really need help. Please and Thank you. :D

-What is the next term of the sequence 9, 6, 4, 8/3, . . . ?
a. 2/3
b. 16/3
c. 8/9
d. 16/9
*I did 4-8/3=4/3. Or would it be 4-1=3.How would I solve this?

-What are the next two terms of the sequence 32, -48, 72, -108, . . . ?
a. -162, 189
b. 162, -189
c. -162, 243
d. 162, -243
*After finding the next terms I chose choice D. Am I right?

-What is S[n] for the arithmetic series with d = -4, an = 27, and n = 9?
a. 360
b. 387
c. 418
d. 451
*My answer was 396 but that is not a choice. How would I solve this?

-What are the two geometric terms between 2 and 1/4?
a. 17/12, 5/6
b. 5/4, 1/2
c. 1, 1/2
d. 1, 0
*I chose choice C. Am I right?


-What are the missing terms of the geometric sequence -3, _ , _ , -375?
a. -127, -251
b. 127, 251
c. -15, -75
d. 15, 75
*I chose choice C. Am I correct?
 
-What is the next term of the sequence 9, 6, 4, 8/3, . . . ?
a. 2/3
b. 16/3
c. 8/9
d. 16/9
*I did 4-8/3=4/3. Or would it be 4-1=3.How would I solve this?
Click to expand...

They are being reduced by 2/3rds each time.



-What is S[n] for the arithmetic series with d = -4, an = 27, and n = 9?
a. 360
b. 387
c. 418
d. 451
*My answer was 396 but that is not a choice. How would I solve this?
Click to expand...

\(\displaystyle a_{n}=a_{1}+(n-1)d\)

\(\displaystyle 27=a_{1}+(9-1)(-4)\)

\(\displaystyle a_{1}=59\)

Use \(\displaystyle S_{n}=\frac{n}{2}(a_{1}+a_{n})\)

Just plug in what you are given. It is one of the choices.
 
edd fedds said:
-What are the next two terms of the sequence 32, -48, 72, -108, . . . ?
a. -162, 189
b. 162, -189
c. -162, 243
d. 162, -243

I chose choice D. Looks good, to me. (It would be more fun, if they were to ask for the formula.)

-What is S[n] for the arithmetic series with d = -4, an = 27, and n = 9?
a. 360
b. 387
c. 418
d. 451

*My answer was 396 but that is not a choice. Please show your work. (The answer is B.)


-What are the two geometric terms between 2 and 1/4?
a. 17/12, 5/6
b. 5/4, 1/2
c. 1, 1/2
d. 1, 0

*I chose choice C. Am I right? Looks good, to me.

-What are the missing terms of the geometric sequence -3, _ , _ , -375?
a. -127, -251
b. 127, 251
c. -15, -75
d. 15, 75

*I chose choice C. Am I correct? Looks good, to me.
Click to expand...

If you would like us to check your work, it helps to see your work. :idea:

With many math exercises, it's possible to check solutions yourself. For example, on the last exercise, ratios of adjacent elements must be equal (that's what makes a sequence geometric). So, check to make sure that your choice leads to a constant ratio. If it does, then your choice must be correct.

-3/(-15)
-15/(-75)
-75/(-375)
 
I understand. Thak you so much for all your time and effort. You helped me alot. :mrgreen:
 
Thanks alot for the advice Edith. However, I always do my own homework. These are problems that I use for practice from the back of my textbook or from web sites given to me by my teacher to both prepare me and help me understand more. Problems that I attempted on my own but could not understand are what I post. Believe me, I am very serious about my understanding of my subjects and ask for help when neccessary. If you could offer me any tutoring or understanding in the future I would truly appreciate it.Thank you once again especially for the site that you referenced to me and please understand that this message is in no way intended to offend you, but to let you know that I understand your point of view, and hope you can understand mine as well. For the problems that I get stuck on, I will make more attempts at helping you [tutors] to see what I may need help with. Also, thank you for all the tutors from this site who have helped me in some way or another.I am utterly graceous. And, I apoligize for my improper posts. :)
 
Edd:

Edith is a SPAMMER.

She posts to direct readers to the referenced site, where they will pay $79 per month to take full advantage of services. They will also need to download and install software on their personal computer, to enable voice communications over the Internet (along with who knows what else). Don't trust sites that SPAM; they lack integrity.



Edith:

Get a real job.

 
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