sorry

Ta có:

2OM=OM+OM=(OA+AM)+(OB−BM)=OA+OB+(AM−BM)2OM=OM+OM=(OA+AM)+(OB−BM)=OA+OB+(AM−BM)

Vì M là trung điểm AB

=> AM=BM

=> 2OM=OA+OB2OM=OA+OB

=> OM=OA+OB2

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