Question

solve this problem ​

Answer 1

given a = 1-1/n = n-1/n

d = (n-2/n)-(n-1/n)= -1/n

Sn =n/2{2a+(n-1)d}

n/2{2(n-1/n)+(n-1)(-1/n)}

n/2{2n-2/n -1 +1/n}

n/2{2n-2-n+1/n}

n/2(n-1/n)

1/2× (n-1)