Math Is Fun Forum

All_Is_Number

Member

Registered: 2006-07-10

Posts: 258

Can someone prove this please?

I have to use this formula often in a couple Stat Methods classes, but haven't seen a proof (my text presents formulas, but does not prove them). My own attempts have been unsuccessful and messy. Thus far, I've just taken it on faith that it is true, but I would prefer to know why it's true. Thanks.

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You can shear a sheep many times but skin him only once.

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: Can someone prove this please?

Remember, by definition,

. You can take any constants (such as

) outside of the sigma sign (this is effectively factorising), and each term within the sigma is summed 'n' times.

Also,

. (you can think of it as 'pushing the sigma through'). 

Only click the button below once you've had another go using all of the information I've given

Last edited by Daniel123 (2008-11-02 00:21:57)

All_Is_Number

Member

Registered: 2006-07-10

Posts: 258

Re: Can someone prove this please?

Thank you.

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You can shear a sheep many times but skin him only once.