a)
(125)=5!(12−5)!12!=5!⋅7!12⋅11⋅10⋅9⋅8⋅7!=5⋅ 4 ⋅ 3 ⋅2⋅112⋅11⋅10⋅9⋅8= 5 ⋅ 2 11⋅10⋅9⋅8=11⋅9⋅8=792
(88)=8!(8−8)!8!=0!1=11=1
(62)=2!(6−2)!6!=2!⋅4!6⋅5⋅4!=2⋅16⋅5=230=15
(230)=0!(23−0)!23!=1⋅23!23!=1
b)
(82)=2!(8−2)!8!=2!⋅6!8⋅7⋅6!=2⋅18⋅7=256=28
(86)=6!(8−6)!8!=6!⋅2!8⋅7⋅6!=2⋅18⋅7=256=28
(101)=1!(10−1)!10!=1⋅9!10⋅9!=10
(109)=9!(10−9)!10!=9!⋅1!10⋅9!=110=10
c)
(72)⋅(42)=2!(7−2)!7!⋅2!(4−2)!4!=2!⋅5!7⋅6⋅5!⋅2!⋅2!4⋅3⋅2!=2⋅17⋅6⋅2⋅14⋅3=242⋅212=21⋅6=126
(124)⋅(53)=4!(12−4)!12!⋅3!(5−3)!5!=4!⋅8!12⋅11⋅10⋅9⋅8!⋅3!⋅2!5⋅4⋅3!= 4 ⋅ 3 ⋅ 2 ⋅112⋅11⋅105⋅9⋅2⋅15⋅4=495⋅220=495⋅10=4950
(145)⋅(123)=5!(14−5)!14!⋅3!(12−3)!12!=5!⋅9!14⋅13⋅12⋅11⋅10⋅9!⋅3!⋅9!12⋅11⋅10⋅9!=5⋅ 4 ⋅ 3 ⋅2⋅114⋅13⋅12⋅11⋅10⋅ 3 ⋅ 2 ⋅1122⋅11⋅10= 5 ⋅ 2 14⋅13⋅11⋅10⋅2⋅11⋅10=14⋅13⋅11⋅220=2002⋅220=440 440
(63)⋅(95)=3!(6−3)!6!⋅5!(9−5)!9!=3!⋅3!6⋅5⋅4⋅3!⋅5!⋅4!9⋅8⋅7⋅6⋅5!=3⋅2⋅16⋅5⋅4⋅4⋅3⋅2⋅19⋅8⋅7⋅62=5⋅4⋅9⋅7⋅2=2520