The radius of the circle having. $$3 x-4 y+4=0$$ and $$6 x-8 y-7=0$$ as its tangents is

A circle is such that $$(x-2) \cos \theta+(y-2) \sin \theta=1$$ touches it for all values of $$\theta$$. Then, the circle is

The least distance of the point $$(10,7)$$ from the circle $$x^2+y^2-4 x-2 y-20=0$$ is

Suppose that the $$x$$-coordinates of the points $$A$$ and $$B$$ satisfy $$x^2+2 x-a^2=0$$ and their $$y$$-coordinates satisfy $$y^2+4 y-b^2=0$$. Then, the equation of the circle with $$A B$$ as its diameter is