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ADCBO ------------- , ADCB , ABCD AC BC O , AO = CO, BO = DO.OADCB(1) AB DC AC , BAC = ACD () AB DC BD

, BDC = ABD, AOB COD () OAB = OCD, OBA = ODC AB = BC , AOB ~ COD , AO = CO BO = CO () [ ][ ]

[ -- ]=o PSRQOPQRS PR QS O , POS ~ QOR.

= () ?() ?

(3) ? ADCB ABCD () ?() , O () AC = b ,BD = a , ABCD O