# Sigma Help?

• Jul 28th 2010, 11:28 AM
habibixox
Sigma Help?
Hi :)
I forgot how to solve sigma problems and these are one of the last problems I need to solve for my AP Calc summer assignment. If someone could help, I would greatly appreciate it:)

The directions say to expand and simplify:

a)

4
E n2 / 2
n=0

b)
1
E 1/n^3
n=1

I am pretty sure you start off with substituting (n=..) for n but how would I continue the problem?

Thanks for helping!(Hi)(Happy)
• Jul 28th 2010, 11:34 AM
skeeter
Quote:

Originally Posted by habibixox
Hi :)
I forgot how to solve sigma problems and these are one of the last problems I need to solve for my AP Calc summer assignment. If someone could help, I would greatly appreciate it:)

The directions say to expand and simplify:

a)

4
E n2 / 2
n=0

b)
1
E 1/n^3
n=1

if I interpreted your first summation correctly ...

$\displaystyle \sum_{n=0}^4 \frac{n^2}{2} = \frac{1}{2} \sum_{n=0}^4 n^2 = \frac{1}{2}(0^2 + 1^2 + 2^2 + 3^2 + 4^2)$

get the idea?
• Jul 28th 2010, 11:42 AM
habibixox
Awesome! Yes, I do, thank you :)
It refreshed my memory :P

so would the second one be this?

1
E 1/n^3
n=1

1
1E n^3 = 1(0^2 + 1^2) = 1?

n=1
• Jul 28th 2010, 11:54 AM
skeeter
Quote:

Originally Posted by habibixox
Awesome! Yes, I do, thank you :)
It refreshed my memory :P

so would the second one be this?

1
E 1/n^3
n=1

1
1E n^3 = 1(0^2 + 1^2) = 1?

n=1

incorrect.

$\displaystyle \sum_{n=1}^1 \frac{1}{n^3} = \frac{1}{1^3} = 1$

you need some review on your own ...

Algebra II Recipe: Using Summation Notation
• Jul 28th 2010, 12:07 PM
habibixox
Quote:

Originally Posted by skeeter
incorrect.

$\displaystyle \sum_{n=1}^1 \frac{1}{n^3} = \frac{1}{1^3} = 1$

you need some review on your own ...

Algebra II Recipe: Using Summation Notation

thank you for your help! it means a lot :) I reviewed that website, and searched for other practice problems. Thanks again! :)