Points B=B1,B2,⋯,Bn,Bn+1=C are chosen on side BC of a triangle ABC in that order. Let rj be the inradius of triangle ABjBj+1 for j=1,⋯,n , and r be the inradius of △ABC. Show that there is a constant λ independent of n such that :
(λ−r1)(λ−r2)⋯(λ−rn)=λn−1(λ−r)