Question

The sum of first n terms of A.P. is $3n+n^2$ then

Find sum of first two terms.

Answer 1

Here $S_n=3n+n^2$

Now, first term $a=S_1\Rightarrow a=3\times 1+1^2=4$ and

Sum of first two terms $=S_2=3\times 2+2^2=10$