How to prove 1x2 + 2x3 + +n(n+1)=n(n+1)(n+2)/3 By the way, 1x2 + 2x3 + +n(n+1)（n+2）=n(n+1)(n+2)(n+3)/4

How to prove 1x2 + 2x3 + +n(n+1)=n(n+1)(n+2)/3 By the way, 1x2 + 2x3 + +n(n+1)（n+2）=n(n+1)(n+2)(n+3)/4

Prove 1x2 + 2x3 + +n(n+1)=n(n+1)(n+2)/31x2+2x3+… +N (n + 1) = 1x (1 + 1) + 2x (2 + 1) +. + n (n + 1) = (1 ^ 2 + 2 ^ 2 +. + n ^ 2) + (1 + 2 +. + n) = n (n + 1) (2n + 1) / 6 + n (n + 1) / 2 = n (n + 1) (n + 2) / 3 prove 1x2 + 2x3 + +N (n + 1) (n + 2) = n (n + 1) (n + 2) (n + 3) / 4 is wrong, I

What's the nth number? 1 and 1 / 2, 2 and 2 / 3, 3 and 3 / 4, 4 and 4 / 5 2+2~2+2~3+…… +2~n

N and N / (n + 1)

A question to find a rule: 1, - 2,3, - 4 What is the nth number of - 1,2, - 3,4?

[（-1）^（n+1）]n
[（-1）^n]n