Toán Lớp 6: Kí hiệu n! = 1 . 2 . 3 …. n
Tính S = 1.1! + 2.2! + 3.3! + 4.4! + …. + 10.10!
Leave a reply
Register Now
Login
Lost Password
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Toán Lớp 6: Kí hiệu n! = 1 . 2 . 3 …. n
Tính S = 1.1! + 2.2! + 3.3! + 4.4! + …. + 10.10!
Comments ( 1 )
Ta có : n.n! = [ ( n + 1 ) – 1 ] – n!
= n! . ( n + 1 ) – n! = ( n + 1 )! – n!
Vậy S = ( 2! – 1! ) + ( 3! – 2! ) + ( 4! – 3! ) + …. + ( 11! – 10! )
= 1! + 2! – 2! + 3! – 3! + 4! – …. – 10! + 11!
= 11! – 1
⇒ S = 11! – 1
hieudz6