Question

Equation for sum of arithmetic progression

Answer 1

This is an example of an arithmetic progression (AP) and the constant value that defines the difference between any two consecutive terms is called the common difference. The sum of an arithmetic series of n terms is found by making n/2 pairs each with the value of the sum of the first and last term.

Answer 2

Sn= n/2( 2a+(n-1) d) or
Sn= 2a+l
  where a is the first term, d is the common difference and l is the last term