Question

the first term and second term middle term is a b c then sum of all terms is

Answer 1

Here,a=a

and,d=b-a

therefore Sn=n/2{2a+(n-1)d}

by putting above values we get...

=n/2{2a+(n-1)(b-a)

=n/2{2a+bn-an-b+a}

=n/2{3a+b+bn-an}

Answer 2

a+b+c
is answer because its asking sum