question on recovering numerical factors from rational polynomials

K=(25*x^2 + 100*y*x + 100*y^2)/(49*x^2 - 98*y*x + 49*y^2)
? factor(K)
%9 =
[  x - y -2]

[x + 2*y  2]

why isn't this

[       5  2]

[       7 -2]

[ x-y    -2]

[x+2y   2]

using content on the rational poly can sometimes lead to problems if a 
variable is in common with the terms.

how do I recover the rational number (5/7)^2 ?

Randall