A. ax cosθ+by sinθ=a2 cos4+b2 sin4θ

B. ax cosθ-by sinθ=a2 cos4-b2 sin4θ

C. x/acosθ+y/b sinθ=1

D. x/acosθ-y/b sinθ=1

The distance between the limiting points of the coaxial system x^{2} + y^{2} – 4x – 2y – 4 + 2λ(3x + 4y + 10)=0

The condition that the pair of tangents drawn from the origin to the circle x^{2}+y^{2}+2gx+2fy+c=0 may be at right angles is

The equation of the chord of the circle x^{2}+y^{2}+16x+2y+10=0 parallel to the chord x-3y-15=0 and which is at the same distance from the centre is

If the tangent to the circle x^{2}+y^{2}=5 at (1, -2) also touches the circle x^{2}+y^{2}-8x+6y+20=0, then the point of contact is

The radical centre of the circle x^{2}+y^{2}+a_{r}x+b_{r }y+c=0, r=1, 2, 3 is