(m-n)^2+4mn m^2-2mn+n^2+4mn (m+n)^2
------------------=---------------------------------=---------------
2mn(m-n) 2mn(m-n) 2mn(m-n)
7p+q p-7q 7p+q 7q-p 7pq+q^2+7pq-p^2 (q-p)(q+p)+14pq
-------- + ------------=-------- + -----------=-------------------------= --------------------
p(p-q) q(q-p) p(p-q) q(p-q) pq(p-q) pq(p-q)