Question

in the formula Sn=n/2(2a+(x-1)d) what is the value of"n" and "x"

Answer 1

n and X are the same
and they both represent no.of terms in an A.P.

Answer 2

Ur formula is slightly wrong
The correct one is:
Sn=n/2(2a+{n-1},×d
where n is the number of terms