Question

If the sum of the first n terms of an AP is 4n − n 2 , what is the first term (that is S1)? What is the sum of first two terms? What is the second term? Similarly find the 3 rd , the10 th and the n th terms.

Answer 1

Step-by-step explanation:

by using formula

an = 4n-n^2 (given in question)

on putting the value of n as 1

we get, a1= 4 -1

=3

on putting 2 on the place of n

we get, a2 =8- 4

=4

now the AP is

3,4,5,6,7,8.......

so, the S1= 3

and, S2 =7

the 2nd term is 4

3rd term is 5

and 10th term is 12

and the nth term

Sn=n(2a+(n-1)d)

2