Question

Formula for sum of A.P

Answer 1

Sn = a + (n-1)d

where 'a' is the first term and 'd'  is the common difference

and Sn is the nth term of the ap

Answer 2

the formula for series A.P is
$S_n= \frac{n}{2}(a+l)= \frac{n}{2}(2a+(n-1)d)$
where n is the no. of terms
     a is first term
    l is the nth term
       d is the common difference