Hi, I am struggling with this problem

. I do not know the properties of circles so well, so I gave the variables some values and drew, but I still don't get anything :-/. It would also be great if you could tell me how you know (what rule, etc.) you have used to answer the question. Thanks!

The problem says:

Let $\displaystyle ax^2+ay^2+kx+ly+m=0$, $\displaystyle bx^2+by^2+px+qy+r=0$ be two intersecting circles. Deviding the first equation by a and the second by b and subtracting, we obtain the equation of a line:

$\displaystyle (k/a-p/b)x+(l/a-q/b)y+(m/a-r/b)=0$.

What is this line?