000RM.dvi

26.2 A relation among the radii 713

26.2 A relation among the radii ...........

ra+rb+rc=4R+r.

ra

r

rc

rb

D

I

A

B C

Ic

Ia

Ib

O

M

M′

ra−r=2DM′,

rb+rc=2MD=2(2R−DM′);

ra+rb+rc−r=4R.