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**Au101****Member**- Registered: 2010-12-01
- Posts: 353

Hello everyone,

So, I've been away from maths for a while and - since I've missed it - I decided I wanted to brush up on my calculus a bit, which has deteriorated rather a lot. Anyway, I've been reading through an old textbook of mine and I've come across the line:

I don't know if I'm just missing an obvious fact since everything's a bit slow and clunky for me these days, but I can't see where the second line comes from and was hoping someone might be able to explain it to me. Thanks

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 15,955

Hi Au101

It is a well-known identity:

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**Au101****Member**- Registered: 2010-12-01
- Posts: 353

Ahhh thank you anonimnystefy, now I see, because of course

And then all the terms in between cancel That's a great help

*Last edited by Au101 (2013-06-05 07:03:46)*

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 15,955

That is correct! You are welcome!

If there's anything else, just ask.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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