OD平分∠BOC,
∠DOC=(1/2)∠BOC
OE平分∠AOC,
∠EOC=(1/2)∠AOC
∠DOE=∠DOC+∠EOC=(1/2)∠BOC+(1/2)∠AOC
=(1/2)(∠BOC+∠AOC)
=1/2*180°
=90°
∴OD⊥OE