This is my first question here, so please tell me if the question is too trivial for this location. I have read FAQ and I didn't find the rule against easy questions :)
I should construct a system of linear equation similar to this one:
$\begin{align}x+2y & = 4 \\ 5x-y & = \frac15\end{align}$
It is suggested that similarity should be in relation between coefficients. All that I see is that if we put it in form $y=ax+b$, it is true that $ab=-1$.
Any hints?