If the equation of the curve is

$\displaystyle

ax^2+2hxy+by^2+2gx+2fy+c=0

$

and this curve is such a conic that the focus lies on the directrix.

Can anybody describe the possible situations i.e what happens if $\displaystyle h^2-ab$ is $\displaystyle >,<$ or $\displaystyle =$ to 0(zero)

Or

Can anybody provide a link where such a situation has been described.

Thanks in advance.