Question

if the sum of the first n terms of an AP is 4n-n²,what is the first term (that is S1)?What is the sum of first two terms?what is the second term?similarly,find the 3rd,the 10th and the nth terms.

Answer 1

Given that,

Sn = 4n − n2



First term, a = S1 = 4(1) − (1)2 = 4 − 1 = 3





Sum of first two terms = S2

= 4(2) − (2)2 = 8 − 4 = 4

Second term, a2 = S2 − S1 = 4 − 3 = 1

d = a2 − a = 1 − 3 = −2

an = a + (n − 1)d

= 3 + (n − 1) (−2)

= 3 − 2n + 2

= 5 − 2n

a10 = 5 − 2(10) = 5 − 20 = −15

@skb

Answer 2

Hey friend ☺ here is ur answer ___________________________

First term = 3
Sum of first two terms = 4
Second term = 1

Hope this helps u..