The nth term of an A.P is given by . Find the sum of first terms of this A.P.

As per the given information,

The n^th term of the A.P

So, by putting the value of  n  as and  we can find the first and 20^th term of the A.P,

And,

Now, for finding the sum of 20 terms of this A.P we have the first and last term as and

So, using the formula of sum of n terms of A.P

Therefore, the sum of first 20 terms of this A.P. is .