Questions in pair-st-lines

Select	Question
	The equation $12{{x}^{2}}+7xy+a{{y}^{2}}+13x-y+3=0$ represents a pair of perpendicular lines. Then the value of ‘a’ is
	The angle between the lines ${{x}^{2}}+4xy+{{y}^{2}}=0$ is
	If the equation $12{{x}^{2}}+7xy-p{{y}^{2}}-18x+qy+6=0$ represents a pair of perpendicular straight lines, then
	The angle between the pair of lines represented by $2{{x}^{2}}-7xy+3{{y}^{2}}=0$, is
	If the angle $2\theta $is acute, then the acute angle between ${{x}^{2}}(\cos \theta -\sin \theta )+2xy\cos \theta +{{y}^{2}}(\cos \theta +\sin \theta )=0$ is
	If the angle between the pair of straight lines represented by the equation ${{x}^{2}}-3xy+\lambda {{y}^{2}}+3x-5y+2=0$ is ${{\tan }^{-1}}\left( \frac{1}{3} \right)$, where $'\lambda \,'$is a non negative real number. Then$\lambda $is
	The angle between the lines ${{x}^{2}}-xy-6{{y}^{2}}-7x+31y-18=0$ is
	The line $x-2y=0$will be a bisector of the angle between the lines represented by the equation ${{x}^{2}}-2hxy-2{{y}^{2}}=0$, if $h=$
	The equation of the bisectors of the angle between lines represented by equation $4{{x}^{2}}-16xy-7{{y}^{2}}=0$is
	The equation of the bisectors of angle between the lines represented by equation ${{(y-mx)}^{2}}={{(x+my)}^{2}}$is