Question

38. If the sum of n terms of an A.P is given by Sn = 3n? + 4n. Determine the A.P
and the nth term.​

Answer 1

★ Answer :

Sum of nth term of the A.P 3n² + 5n

Putting n as 1 we will get first term (a).

→ a (S1) = 3(1)² + 5(1)

→ a = 3 + 5

→ a = 8

$\rule{200}{2}$

Putting n as 2 we will sum of first two numbers.

→ S2 = 3(2)² + 5(2)

→ S2 = 3(4) + 10

→ S2 = 12 + 10

→ S2 = 22

$\rule{200}{2}$

Now, Let second term of A.P be a2.

→ S2 = a + a2

→ 22 - 8 = a2

→ a2 = 14

$\rule{200}{2}$

Let common difference be D.

→ D = a2 - a1

→ D = 14 - 8

→ D = 6

So, A.P = 8, 14, 20, 26, 32 .........