2nd order displacement

Discussion in 'Math' started by boks, Apr 18, 2010.

  1. boks

    Thread Starter Active Member

    Oct 10, 2008
    218
    0
    One dimensional linear atomic chain with
    two different atoms of masses m and M.
    Atoms are connected by springs of spring
    constants K. The lattice constant is a.

    [​IMG]

    Can anyone explain the last step?
     
  2. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Looks like algebra, collection of like terms.
     
  3. Fraser_Integration

    Member

    Nov 28, 2009
    142
    5
    yeah, there were two separate u(sub)n terms, so they just collected them
     
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