- #1

{ imp }

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## Homework Statement

Hello, I was reading Feynman's lectures on physics, and I'm having trouble following some deductions in the part about Probability. The random walk is a problem in which someone starts at x = 0 ant then takes a step forward (x = 1) or backward (x = -1) and after N steps de distance traveled is D

_{N}. I'll atach the images regarding the problem because it's kind of large.

I don't really understand how does he get to the part

D

_{N}

^{2}= N

How is that?

## Homework Equations

They are all on the images.

## The Attempt at a Solution

I'm thinking about <D

_{N-1}

^{2}> = N - 1, but I don't know why would that be.

I'm sorry if this doesn't go here or if my post is a little hard to read. Thanks in advance.