Question

if sn the sum of first n terms of an AP is given by sn =3n sq. -4n ,find the nth term.​

Answer 1

Step-by-step explanation:

taking n = 1, S1 = a1 = -1

taking n = 2, a2 = S2 - S1 = 4 + 1 = 5

so, d = +6

therefore, an = a + (n-1)*d

= -1 + 6n - 6

= 6n -7

Answer 2

Answer:

6n - 7

Step-by-step explanation:

Given sum of n terms is

Sn = 3n² - 4n

= 3n²-6n+3-4n+4

= 3n²-10n+7

Sum of n terms is = sum of n-1 terms + nth term.

=> nth term = Sn - Sn-1

= 3n²-4n-(3n²-10n+7)

= 6n-7