- #1
darkchild
- 155
- 0
Homework Statement
From Landau and Lifgarbagez:
[tex]\langle (\Delta f)^{2} \rangle = \overline{f^{2}} - (\overline{f})^{2}[/tex]
This isn't derived, just stated, and I'd like to understand how it comes about. f is a generic quantity "relating to a macroscopic body or to a part of it."
Homework Equations
[tex]\Delta f = f - \overline{f}[/tex]
The Attempt at a Solution
[tex](\Delta f)^{2} = (f-\overline{f})^{2} = f^{2} - 2f \overline{f} + \overline{f}^{2}[/tex]
Basically, I don't know how to do the averaging (not without explicit values of f, anyhow).