<Tri-2026-2330>, hint

Since AH=2R cosA, OD= RcosA, AH//OD, triangles POD and PAH are similar

By vectors OG=1/3(OA+OB+OC) . 

since  IOAI=IOPI, OP=-OA, OH=OA+OB+OC, OG'=OA+OP(-OA)+OH(OA+OB+OC)=1/3(OA+OB+OC). Hence G=G'

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