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

If the equation $2x^2 + 7xy + 3y^2 - 9x - 7y + k = 0$ represents a pair of lines,then $k$ is equal to

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

If $x^2-y^2+2hxy+2gx+2fy+c=0$ is the locus of a point which moves such that it is always equidistant from the lines $x+2y+7=0$ and $2x-y+8=0$,then the value of $g+c+h-f$ equals

If the equation $x^2 + y^2 + 2gx + 2fy + 1 = 0$ represents a pair of straight lines,then:

The equation $x^2 + kxy + y^2 - 5x - 7y + 6 = 0$ represents a pair of straight lines,then $k$ is