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HoangAnhThuxinhvcd hasn't added any friends yet.
12-09-2023 - 22:55
do a,b,c>=1 nên a,b,c<=4 có (a-1)(b-1)>=0 nên ab>=a+b-1 cmtt, => P>=sigma a+b-1/c+6=5-c/c+6
đến đây dùng uct để đánh giá: 5-c/c+6>=mc+n( thay dấu bằng c=1,c=4)