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- Jun 11th 2011, 12:09 AMPunchMethod of Difference
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- Jun 11th 2011, 12:28 AMTheCoffeeMachine
Sum ranges from r =1, not n =1, right? It's equivalent to:

- Jun 11th 2011, 01:02 AMPunch
- Jun 11th 2011, 01:46 AMTheCoffeeMachine
- Jun 11th 2011, 06:11 AMSoroban
Hello, Punch!

Quote:

Write out the terms . . .

. . . .

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

. . . .

And we have: .

. . . . . . . . . . .

Therefore:.