It can be proved that six small triangles are congruent.

(2) Since the distance from point O to three sides is equal (S Yin =Sofc+Soch), it is assumed that OD passes through BC and F, and OE passes through AC and G, as long as it is proved that FC+CG is equal to the side length of a triangle.

It can be proved that the passing angles of triangle ODC and triangle AOG are identical, that is, DC=AG, that is, FC+CG=AC.