The lines represented by $ax^2 + 2hxy + by^2 = 0$ are perpendicular to each other,if ........

The acute angle between the lines $6x^2 + 11xy - 10y^2 = 0$ is

The angle between the pair of lines represented by $2x^2 - 7xy + 3y^2 = 0$ is .....$^o$.

The angle between the pair of straight lines $x^2 - y^2 - 2y - 1 = 0$ is....$^o$

The angle between the lines represented by $(\sin ^2 \alpha) y^2 - 2xy(\cos ^2 \alpha) + (\cos ^2 \alpha - 1) x^2 = 0$ is

The combined equation of the two diameters of a circle which divide the circle into $4$ sectors is $ax^2+2hxy+by^2=0$. If the area of the bigger sector is $5$ times the area of the smaller sector,then $\frac{|a+b|}{\sqrt{(a-b)^2+4h^2}} = $