Question

In an A.P nth term is 7n+4; find sn
please explain briefly

Answer 1

look Nth term is given.... u can easily find first term, second term easily by putting 1 ,2 in place of n respectively.... now you have got first term and respective common difference..... now directly apply
s=(n/2)(a+l)
put l =7n+4..and a=7*1+4=11