Đặt A = 1.2.3 + 2.3.4 + 3.4.5 + ... + 28.29.30

4A = 1.2.3.(4-0) + 2.3.4.(5-1) + 3.4.5.(6-2) + ... + 28.29.30.(31-27)

4A = 1.2.3.4 - 0.1.2.3. + 2.3.4.5 - 1.2.3.4 + 3.4.5.6 - 2.3.4.5 + ... + 28.29.30.31 - 27.28.29.30

4A = 28.29.30.31 - 0.1.2.3

4A = 28.29.30.31

\(A=\frac{28.29.30.31}{4}=7.29.30.31=188790\)

Theo cách tính trên ta dễ dàng tính được:

1.2.3 + 2.3.4 + 3.4.5 + ... + (n - 1).n.(n + 1) = \(\frac{\left(n-1\right).n.\left(n+1\right).\left(n+2\right)}{4}\)

bang 719 tick nha  phạm quang huy va cac bn hay tick cho mk voi nha

 nha bạn

1.1!+2.2!+3.3!+4.4!+5.5!=1x1+2x1x2+3x1x2x3+4x1x2x3x4+5x1x2x3x4x5

=1+4+18+96+600

=719

1.1!+2.2!+3.3!+4.4!+5.5!=1.1+2.2+3.6+4.24+5.120

=1+4+18+96+600

=719

^{sai rồi} 

^{vừa làm xong}

719

 Tích chio mình nhé

Hẹdjrjrjdjdjdjjdjdbkrfkfbkncbkfnkkdnkfnndkdbdndkdkdjndkdkdjo2huudjdjod

1!+2.2!+3.3!+4.4!+5.5! 
=(2-1).1!+(3-1).2!+(4-1).3!+ (5-1).4!+(6-1).5! 
=2!-1!+3!-2!+4!-3!+5!-4!+6!-5! 
=6!-1!=720-1=719 

mk tl nhé

1.1!+2.2!+3.3!+4.4!+5.5! 
=(2-1).1!+(3-1).2!+(4-1).3!+ 
(5-1).4!+(6-1).5! 
=2!-1!+3!-2!+4!-3!+5!-4!+6!-5! 
=6!-1!=720-1=719 

100% trên vio