Aw shiat, any chance anyone awake that is knowledgeable in Calculus 2??? In desperate need of help.

[Hoeboy]

Studying for finals and I'm stuck in testing for convirgence and divergence. The book did a step in several problems that I completely do not understand. If ya still remember something about conv/div, respond and I'll post the problem up quick. Thanks.

 

[zayened]

what's up...ratio test or nth term?

what's the question 😉

 

[Aelus]

post your problem, i've seen some of this stuff a couple of years ago, and i might be able to provide help.

Aelus

 

[Hoeboy]

Okay here is 1 problem with the steps but I don't understand one of the steps. Assume it has the sum sign with n=1 to infinity 🙂

1) (-1)^n * n^3
--------------------
3^n

Test for abs. convirg.

So they use the ratio test:

| (-1)^n+1 (n+1)^3| | 3^n |
|------------------------| * |-----------------| So you divide or reverse multiply
| 3^n+1 | | (-1)^n n^3 |


Then they get

1
-- ( n+1 / n )^3
3

I understand that the -1^n+1 and -1^n cancels because it's in absolute so it don't matter. But how the hell they cancel out all the other numbers???


aw crap the spacing is all messed up. can you guys understand?

 

[zayened]

1) (-1)^n * n^3/3^n Test for abs. convirg.

So they use the ratio test:

| (-1)^n+1 (n+1)^3| | 3^n |
|------------------------| * |-----------------| So you divide or reverse multiply
| 3^n+1 | | (-1)^n n^3 |


Then they get

1
-- ( n+1 / n )^3
3

alright...3^n cancel's w/3^n+1, it's just like having 3*3*3*3*3/3*3*3*3*3*3, you have one more three on the bottom, so all the top 3's go away and just leaves the bottom 3

and what you have left is (n+1)^3 on the top and n^3 on the bottom, all they did is put the ^3 sign outside the paranthasees



whew, i HOPE the questions are going to be this easy on Thursday :Q

 

[ItsStillUS]

Math only has numbers. Not letters. You confuse me.

 

[Aelus]

Ack, as i expected, it's been too long since i had this stuff, and i can't look it up because i've got to run for my math class soon. But if you haven't had an answer in 5 hours, i'll look it up and try to help you.

Aelus

 

[Hoeboy]

it's easy because these are examples from the book 😉 ok here's another one but i did it in paint. much easier to look at.

http://www.geocities.com/definition80/asdf.GIF

 

[zayened]

i got your answer bro...read my 2nd post

 

[Hoeboy]

oh yeah. drag the link to the address bar to load the pix. yahoo is funky that way.

 

[jbahseng]

<< it's easy because these are examples from the book 😉 ok here's another one but i did it in paint. much easier to look at.

http://www.geocities.com/definition80/asdf.GIF >>



(n+1)^(n+1) = (n+1)^n * (n+1)^1

eg.

2^3 = 2^2 * 2^1
8 = 4 * 2
= 8

 

[Hoeboy]

ah silly me. sometimes you get caught up in too much calc and forget your basic arithmatic. thanks guys. back to the books 😉 goodluck on all your finals.