? AC BC AB r L s Figure A 2.02.02.00 6.0 1.7 (or 1.8) Figure B3.04.05.01.012.06.0.
(2) According to the chart information, r=2SL (or 2s=Lr) is obtained, which is true for general triangles.
It is proved that in any △ABC, ⊙O is the inscribed circle of △ABC, and it is obtained by connecting OA, OB and OD.
S= 12BC？ r+ 12AC？ r+ 12AB？ r= 12Lr
∴r=2SL.
Update 1: Excuse me, I want a book suitable for senior pupils.
Title: Fight and Abandon Author: Zheng Yongchang Introduction: This book is a special study of Si