For the standard conic equation in 2-D plane i.e $$ax^2 + 2hxy + by^2 +2gx +2fy +c =0$$ If $a=b=0$ and $h\neq 0$, then the equation reduces to $$2hxy + 2gx + 2fy + c =0$$
Under what conditions will the above equation represent a pair of straight lines?