The angle between the pair of lines cos2θx2+2xy sinθ+sin2θ−1=0is

The condition that two lines represented by the equation ax2+2hxy+by2=0 are to be perpendicular is  a+b=0For the equation cos2θx2+2xysinθ+sin2θ−1=0 , the values  a=cos2θ,b=sin2θ−1Consider a+b=cos2θ+sin2θ−1=1−1=0Since, a+b=0,the angle between the lines is π2.