a) 13! = 13.12.11....5.4.3.2.1 => 13! chia hết cho 2 và 5
11! = 11.10.9....5.4.3.2.1 => 11! chia hết cho 2 và 5
=> A = 13! - 11! chia hết cho 2 và 5
c) A = 13! - 11! = 13.12.11! - 11! = (13.12 - 1) .11! = 155.11! chia hết cho 155
Vậy A chia hết cho 155
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bài làm
a,b) 13! = 13.12.11....5.4.3.2.1
=> 13! chia hết cho 2 và 5
11! = 11.10.9....5.4.3.2.1
=> 11! chia hết cho 2 và 5
=> A = 13! - 11! chia hết cho 2 và 5
c) A = 13! - 11! = 13.12.11! - 11!
= (13.12 - 1) .11!
= 155.11! chia hết cho 155
Vậy .............
hok tốt
