Question 903012
S = n/2[2a+(n-1)d]
(2/n)S = [2a+(n-1)d]
2S/n = 2a + (n-1)d
2S/n - 2a = (n-1)d
{{{(2S/n - 2a)/(n-1)}}}= d
0r
{{{(2S - 2an)/n(n-1)}}}= d