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# Sum watch

1. How do I prove that,

I have done this:

Thanks.
2. Take out as a factor and then simplify the quadratic that you're left with.
3. Following on from yours
n(n+1)(n(n+1)-6)
n(n+1)(n^2+n-6)
n(n+1)(n+3)(n-2)
4. (Original post by doivid)
Following on from yours
n(n+1)(n(n+1)-6)
n(n+1)(n^2+n-6)
n(n+1)(n+3)(n-2)
How did you got rid of the minus?
5. (Original post by lnx)
How did you got rid from the minus?
Are you reading n-2 as n+2? As far as I can tell, no-one got rid of a minus (or needed to get rid of a minus).
6. (Original post by nuodai)
Are you reading n-2 as n+2? As far as I can tell, no-one got rid of a minus (or needed to get rid of a minus).
lol nah, but

if you divide this by n(n+1), wouldnt yuo get n(n+1)-6?
7. (Original post by lnx)
lol nah, but

if you divide this by n(n+1), wouldnt yuo get n(n+1)-6?
Yes... which is what doivid said
8. (Original post by nuodai)
Yes... which is what doivid said
How did he get: n(n+1)(n(n+1)-6)
9. (Original post by lnx)
How did he get: n(n+1)(n(n+1)-6)
I really can't see why you're confused here You have right? I'll go through it in extremely small steps:

So:
10. (Original post by lnx)
How did he get: n(n+1)(n(n+1)-6)

expand the brackets

n(n+1) * n(n+1) gives you your n^2(n+1)^2 and n(n+1) * -6 gives you your -6n(n+1).
11. (Original post by lnx)
if you divide this by n(n+1), wouldnt yuo get n(n+1)-6?
(Original post by lnx)
How did he get: n(n+1)(n(n+1)-6)
12. haha ah okay, sorry guys for the confusion and thanks noudai for the steps.

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