Question

If the sum of first n terms of an Ap is 4n-n²,what is
the first term,second term and nth term

Answer 1

Sn = 4n − n2



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

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