Question

what is the sum of first nerms of an ap

Answer 1

Sum of n terms of AP is n/2(a+l).

Answer 2

we all know in Ap is we have common difference d

lets say first term a second term a1= a+d third term a2= a+2d ....nth term an= a+(n-1)d

sum of these= a+a1+a2+...an= a+a+2d+a+3d......+a+(n-1)d-----1 rewrite terms in reverse order         s= [a+(n-1)d]+[a+(n-2)d]+....+a] ----2

add 1 and 2   2s= n[2a+(n-1)d]

sum = n/2 [2a+(n-1)d]