Question

if Sn the sum of first n terms of an A.P. is given by Sn= 3n^2-4n then, find its nth term and common difference.​

Answer 1

Explanation:

Arithmetic Progressions. If Sn, the sum of first n terms of an A . P. is given by Sn = 3n2 – 4n, then find its nth term. Hence, required nth term is 6n – 7.

Answer 2

Explanation:

Sn = 3n^2 - 4n

n = 1

S1 = (3× 1)^2 - 4×1

= 9 - 4

= 5

n = 2

S2 = (3×2)^2 -4×2

= 6^2 - 8

= 36 - 8

= 28

a = 5

a2 = S2 -S1

=28 - 5

= 23

d = a2 - a

= 23 - 5

= 18

nth term = a + ( n -1 ) d

= 5 +(n -1 ) 18

= 5 + 18n - 18

= 18n - 13

so nth term is 18n - 13.

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