Im confused..Is it a+ or a- for the first formula?there is one that finds the nth term of a sequence in AP --> l=a+(n-1)d............ l=last term , a=first term, n=number of terms, d=common difference between terms.
there's one more that finds the sum of terms in AP --> 1/2n(2a+(n-1)d) OR 1/2n(a+l)