Hello, tahsocks!

I'll re-write the problem in a more manageable form.

Recall that is a constant: .

The left side is: .

. .

The right side is: .

. .

. .

The left side and the right side are equal . . .

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- October 8th 2011, 09:29 AM #1

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## Problem

Hi, I've attached an image of this little snippet from a lecture.

I just do not get why this equality holds. It's probably something to do with factorising etc... but I cannot see why.

X bar is the sum of xi over n (i.e. the mean).

My notation is a bit scruffy, but the summation on the left hand side is on the numerator only (not the entire fraction).

Cannot see why it equals 1!?

- October 8th 2011, 11:28 AM #2

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