The equation of the base of an equilateral triangle is $$x+y=2$$ and one vertex is $$(2,-1)$$, then the length of the side of the triangle is

The equation of a straight line which passes through the point $$\left(a \cos ^3 \theta, a \sin ^3 \theta\right)$$ and perpendicular to $$(x \sec \theta+y \operatorname{cosec} \theta)=a$$ is

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

If the lines, joining the origin to the points of intersection of the curve $$2 x^2-2 x y+3 y^2+2 x-y-1=0$$ and the line $$x+2 y=k$$, are at right angles, then $$k^2$$ equals