$A$ homogeneous equation of second degree in $x$ and $y$ represents which of the following?

If the equation $\lambda x^2 + 2y^2 - 5xy + 5x - 7y + 3 = 0$ represents two straight lines,then the value of $\lambda$ is:

If one of the lines given by $k x^2 + x y - y^2 = 0$ bisects the angle between the coordinate axes,then the values of $k$ are

The equation of the pair of lines passing through the point $(2,1)$ and perpendicular to the pair of lines $4xy + 2x + 6y + 3 = 0$ is:

If the equation $2x^2 - 2hxy + 2y^2 = 0$ represents two coincident straight lines passing through the origin,then $h = $

The perpendiculars are drawn to lines $L_1$ and $L_2$ from the origin making an angle $\frac{\pi}{4}$ and $\frac{3 \pi}{4}$ respectively with the positive direction of the $X$-axis. If both the lines are at a unit distance from the origin,then their joint equation is