- #1

- 9

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Write in terms of factorials

n((n^2)-1)

The correct answer is

(n+1)!/(n-2)!

but I don't know how to get there, and since it's week- end I have no chance to ask anyone teachers, etc.

//Martin

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- Thread starter martinrandau
- Start date

- #1

- 9

- 0

Write in terms of factorials

n((n^2)-1)

The correct answer is

(n+1)!/(n-2)!

but I don't know how to get there, and since it's week- end I have no chance to ask anyone teachers, etc.

//Martin

- #2

- 517

- 1

n(n^{2}-1) = n(n-1)(n+1)

- #3

- 9

- 0

Originally posted by martinrandau

Can anybody help me solving this?

Write in terms of factorials

n((n^2)-1)

The correct answer is

(n+1)!/(n-2)!

Please notice the expression marks (!). The task is not to factorise it by "normal" means, but to find an expression as a sequence.

ex. 7! = 1 x 2 x 3 x 4 x 5 x 6 x 7 = 5040

n!= 1 x 2 x 3 x...x n

It's called the factorial r (!).

Thank you for your help anyway!

- #4

Tom Mattson

Staff Emeritus

Science Advisor

Gold Member

- 5,549

- 8

Originally posted by martinrandau

The correct answer is

(n+1)!/(n-2)!

I'll give you a hint.

Expand the numerator and denominator of the above ratio and cancel the factors common to both. For instance, the numerator is:

(n+1)!=(n+1)(n)(n-1)(n-2)...

Get the idea?

- #5

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- 0

Yes!

Thank you!

//Martin

Thank you!

//Martin

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