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, sss -a-b-cABCDEFGH-a-bABCDADEH-b-cABGH-a-c =( -ABCD+ - ADEH + - ABGH) =2(ab+bc+ca)-a-bABCDF-c , 21:16:12 87 .. 5 .., 3 .. 2 .. ? ? 25 , 30 .. 6 10 .., 5 .. 3 ..