If there's anything else, just ask.

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

]]>It is a well-known identity:

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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