The equation $$8 x^2-24 x y+18 y^2-6 x+9 y-5=0$$ represents a

Find the angle between the pair of lines represented by the equation $$x^2+4 x y+y^2=0$$.

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

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