A. (-g, -f)
B. (-f, -g)
C. (-g/2, -f/2)
D. (-f/2, -g/2)
If a circle passes through the point (a, b) and cuts the circle x2+y2=k2 orthogonally, the equation of the locus of its centre is
Let A be the centre of the circle x2+y2-2x-4y-20=0. Suppose that the tangent at the point B(1, 7) and D(4, -2) on the circle meet at the point C. The area of the quadrilateral ABCD is