Question

n(n+1)/2 proof for the formula

Answer 1

Let

S = 1 + 2 + … + (n−1) + n

Now, 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

Hence PROVED....

Hope it helps...

^___^