The lines $ax^2+2hxy+by^2=0$ are at right angles if

If the slope of one of the lines represented by $2x^2 + 3xy + ky^2 = 0$ is $2$,then the angle between the pair of lines is

If the angle between the two lines represented by $2x^2 + 5xy + 3y^2 + 6x + 7y + 4 = 0$ is $\tan^{-1} m$,then $m = $

The angle between the pair of straight lines $x^2 + 4y^2 - 7xy = 0$ is

The equation $x^2-3xy+\lambda y^2+3x-5y+2=0$,where $\lambda$ is a real number,represents a pair of lines. If $\theta$ is the acute angle between the lines,then $\frac{\operatorname{cosec}^2 \theta}{\sqrt{10}} = $

If $(m+3n)(3m+n)=4h^2$,then the acute angle between the lines represented by $mx^2+2hxy+ny^2=0$ is