6! -inseamna 6 factorial, adica inmultesti toate numerele de la 1 pana la 6
5! - inmultesti toate numerele de la 1 la 5
6!x12-5!x12= 1x2x3x4x5x6x13-1x2x3x4x5x12Acum dai factor comun 1x2x3x4x5=120 si vei scrie
(1x2x3x4x5) (6x13-12)=120(78-12)=120x66=7920
b) 5!-1!-2!-3!-4!= 1x2x3x4x5-1-1x2-1x2x3-1x2x3x4=120-1-2-6-24=87
c) 7!-6!+5!-4!=1x2x3x4x5x6x7-1x2x3x4x5x6+1x2x3x4x5-1x2x3x4=
1x2x3x4x5x6 (7-1)+1x2x3x4 (5-1)=
720x6+24x4=4320-96= 4224
