Question

If Sn denotes the sum of n terms of an AP whose common difference is d. What is the value of d.

Answer 1

$S_{n}= \frac{n(2a+(n-1)d)}{2}$
n- number of terms
a-first term of the series
therfore
$d= \frac{\frac{2 S_{n}}{n}-2a}{n-1}= \frac{2 S_{n}-2an}{n(n-1)}$