[急]幾何-定理與證明!

角AOB與角BOC互為鄰補角 : ㄥAOB + ㄥBOC = 180°OD平分角AOB : ㄥAOD = (1/2) ㄥAOB ....(1)OE平分角BOC : ㄥEOC = (1/2) ㄥBOC ....(2)(1) + (2) :ㄥAOD + ㄥEOC = (1/2) ㄥAOB + (1/2) ㄥBOC
ㄥDOE = (1/2) (ㄥAOB + ㄥBOC)
ㄥDOE = (1/2) 180°
ㄥDOE = 90°所以 OD 垂直 OE。