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
1 5 1
thats wrong
its not wrong i bet u
Sn = (n/2)[2a +(n -1)d]
the ans is this
The Brainliest Answer!
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
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