Since logarithms of different bases differ only by a constant depending only on the bases, the base will be omitted and assumed to be 2 unless otherwise noted.

The basic property of logarithm function (for any base):

 log(xy) = log(x) + log(y)
   

      For 
      x = 2a,   log(x) = a
      y = 2b,   log(y) = b

      xy = 2a + b
   

So

      log(xy) = a + b = log(x) + log(y)