If the orthocenter of the triangle formed by the lines $$2 x+3 y-1=0, x+2 y+1=0$$ and $$a x+b y-1=0$$ lies at origin, then $$\frac{1}{a}+\frac{1}{b}$$ is equal to

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