Question

(1+2+3+….......….……………+n/)/n²​

Answer 1

Step-by-step explanation:

Let

S=1+2+…+(n−1)+n.

Write it backwards:

S=n+(n−1)+…+2+1.

Add the two equations, term by term; each term is n+1, so

2S=(n+1)+(n+1)+…+(n+1)=n(n+1).

Divide by 2:

S=

n(n+1)

2