A. x2+y2=c2

B. x2-y2=2c

C. x2-y2=c2

D. none

The point (3, -4) lies on both the circles x^{2}+y^{2}-2x+8y+13=0 and x^{2}+y^{2}-4x+6+11=0. Then the angle between the circles is

The nearest point on the circle x^{2}+y^{2}-6x-4y-12=0 from (-5, 4) is

The equation of the tangents to a circle x^{2}+y^{2}-4x-6y-12=0 and parallel to 4x-3y=1 are

The equation of the chord of the circle x^{2}+y^{2}=25 with (1, -1) as the midpoint is

The equations to the direct common tangents to the circles x^{2}+y^{2}+22x-4y-100=0, x^{2}+y^{2}-22x+4y+100=0is