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What kind of formula is this and how is it to be retraced?

  1. Jan 2, 2016 #1
    This is basic maths but I kind of forgot how to retrace such an equation.
    My question is: why does "+-2*xi(n-1)*delta" which is in the middle of the first long equation cancle out? I'm thankful for an answer!
  2. jcsd
  3. Jan 2, 2016 #2
    The context is missing, but I'll guess that this is random walk?
    For a random walk process, what do you think is the average displacement?
    Another way to look at it would be to consider the [itex]\pm[/itex] signs - how many particles do you think will move in the + direction and how many in the - direction?
    Last edited: Jan 2, 2016
  4. Jan 2, 2016 #3
    Yeah, it is the random walk! :)
    Do you mean that the middle part equals zero (all negatives and positive deltas are on average 0) and that's why it can be canceled out?
    I thought it was some formula like (a+b)(a-b) where it's a²-ab+ab-b² where the inner parts just cancels out each other.
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