The Problem Site : Problem Pages : The Maine Page


Fractional Infinite Series
Find the following sum:

1/(x2+x)
x=1


Problem Moderated by: Douglas
Problem Solution
1/(x^2 + x) =
x=1

1/(x(x+1)) =
x=1

1/x - 1/(x+1)
x=1


(By the method of partial fractions)

This obviously tunnels:
(1/1 - 1/2) + (1/2 - 1/3) + (1/3 - 1/4) ...
leaving just 1.

Or, with more vigor:
n
1/x - 1/(x+1) =
x=1

1 - 1/(n+1)

and the limit of this as n goes to ∞ is 1.

Solution submitted by PdoX

Options
Choose a Page
Login
Join The Site
The Maine Page
Current Problem
Previous Problem
Scores
About This Page

Subscribe
Archives
2006 Problems
2003 Problems
2002 Problems
Problem Pages
Brainfood
High School Math
Calculus
The Maine Page
Games!
Math Games
Word Games
Strategy Games
All Games

The Problem Site : Problem Pages : The Maine Page