
∵c1c2=r1−r2

∴ Given circles are touching internally
Let a variable circle with centre P and radius r
⇒PA=r1−r and PB=r2+r
⇒PA+PB=r1+r2
⇒PA+PB=4(>AB)
⇒ Locus of P is an ellipse with foci at A(0,0) and B(2,0) and length of major axis is 2a=4, e=21
⇒ Centre is at (1,0) and b2=a2(1−e2)=3
if x-axis is the axis of ellipse then

⇒E:4(x−1)2+3y2=1
which is satisfied by (2,±23)