@ @XU@ @ÖïÐaínÜaì@Þî†bjnÜa@ @ . 4! × 5! = 24 ×120 = 2880 () 85 .8! 8 )9 .( 7 8 5 6 . .8!×9×8×7×6×5 () . 10 10 . . . 2(10!)2 .10! ×10! () 3 .