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- June 10th 2011, 11:09 PMPunchMethod of Difference
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- June 10th 2011, 11:28 PMTheCoffeeMachine
Sum ranges from r =1, not n =1, right? It's equivalent to:

- June 11th 2011, 12:02 AMPunch
- June 11th 2011, 12:46 AMTheCoffeeMachine
- June 11th 2011, 05:11 AMSoroban
Hello, Punch!

Quote:

Write out the terms . . .

. . . .

We note that most of the terms cancel out . . .

. . . .

And we have: .

. . . . . . . . . . .

Therefore:.