If the acute angle between the lines given by $$\mathrm{a x^2+2 h x y+b y^2=0}$$ is $$\frac{\pi}{4}$$, then $$\mathrm{4 h^2=}$$

The joint equation of the pair of lines through the origin and making an equilateral triangle with the line $$x=3$$ is

The slope of the line through the origin which makes an angle of 30$$^\circ$$ with the positive direction of Y-axis measured anticlockwise is :

If the equation $$k x y+5 x+3 y+2=0$$ represents a pair of lines, then $$k=$$