Example 1

   T(n) = n^2

   T(5n) = (5n)^2
         = 25n^2
         = 25T(n)

Example 2

   T(n) = n^3

   T(3n) = (3n)^3
         = 27n^3
         = 27T(n)

Example 3

   6n*log(n) + 5n + 2
   => 6n*log(n)       (discarding lower-order terms)
   => n*log(n)        (discarding constant factors)
   => O(n*log(n))