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{ 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 DN. 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
DN2 = N
How is that?
Homework Equations
They are all on the images.
The Attempt at a Solution
I'm thinking about <DN-12> = 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.