Manipulate[o2={1+2*Sqrt[r],r};angle={{0,1},(o2-o1)*1/(1+r)+o1,o2+{0,r}};Graphics[{{Blue,Circle[o1,1]},{Red,Thick,Circle[o2,r]},{FaceForm[Transparent],EdgeForm[{Thick,Magenta}],Rectangle[{0,0},o2+{r,r}]},{Thick,Line[angle]},{Thick,Arrow[{{1,r},angle[[2]]}]},Text[PlanarAngle[angle]/Degree,{0.9`,r}]},AxesTrue],{r,1.,5.},Initialization(o1={1,1})]