(1−r1r2)(1−r1r3)=(1−s−bs−a)(1−s−cs−a)=2
⟹b−as−a⋅c−as−a=2
⟹2(s−a)2=(b−a)(c−a)
⟹(2s−2a)2=2(bc−ac−ab+a2)
⟹(b+c−a)2=2(bc−ac−ab+a2)
⟹b2+c2=a2⟹△ABC is right angled