3×19²+6×1+19×21+3×21²
人气：361 ℃ 时间：2020-03-25 11:53:03
解答
3×19²+6×1+19×21+3×21²
=3(19²+21²+2*19*21)-5*19*21+6
=3*(19+21)^2-5*19*21+6
=4800-5(20-1)*(20+1)+6
=4800-5(20^2-1)+6
=4800-2000+11
=2811
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