I have to determine for which values of parameters p and q the system has indefinite solutions.

System is:

(p-q)x + (3p-5)y = 2pq

(p+q)x + (q-7)y = 6pq

I have solved equation for x:

$\displaystyle x=\frac{18p^2q-24pq-2pq^2}{2pq+q^2+2p-12q+3p^2}$

What next?