27. Exercise problem XXII

If the sum of the first $n$ terms of an AP is $4n − n^2$, what is the first term (that is $S_1$)? What is the sum of first two terms? What is the second term? Similarly find the $3^{\text{rd}}$, the$10^{\text{th}}$ and the $n$th terms.  

 

$S_1=$

 

$S_2=$

 

$a_3=$

 

$a_{10}=$

 

$a_n=$ $i-ii$