Question

Help!!!!!! question from arithmetic progressions...

Answer 1

an = An+B

If we see the general expression for n th term in A.P.,  it is an = a+(n-1)d= a+ nd -d

So the term which is multiplied to n is common difference.

So, by comparing we can say that in the given expression A is the common difference.

Now, n th term is given. So,

First term= (An+B)-{(n-1)d}= (An+B)-{(n-1)A}= (An+B)-{An-A}=An+B-An+A=A+B

Now, sum of n terms= n/2*(a+l) {where l means last term}

So, sum of 20 terms= 20/2*(A+B+An+B)=10*(A+An+2B)= 10*(A+A*20+2B)=10*(21A+2B)


So, answer is 210A+20B.