Answer:

6 (d)

Step-by-step explanation:

If n = 1, S1 = a1 = 3(1)^2 + 4(1) = (3 + 4) = 7

If n = 2, S2 = 3(2)^2 + 4(2) = (12 + 8) = 20

a2 = S2 - S1 = (20 - 7) = 13

d = a2 - a1 = (13 - 7) = 6 (d)

Answer:

U can do this question in very simple steps as told below

Step-by-step explanation:

Let the sum of first n terms of the A.P.=Sn

Given:

S

n

=

3

n

2

–

4

n

...(i)

Now,

Replacing n by (n –1) in (i), we get,

S

n

–

1

=

3

(

n

–

1

)

2

–

4

(

n

–

1

)

nth term of the A.P.

a

n

=

S

n

–

(

S

n

–

1

)

∴

a

n

=

(

3

n

2

–

4

n

)

–

[

3

(

n

–

1

)

2

–

4

(

n

–

1

)

]

⇒

a

n

=

3

[

n

2

–

(

n

–

1

)

2

]

–

4

[

n

–

(

n

–

1

)

]

⇒

a

n

=

3

(

n

2

–

n

2

+

2

n

–

1

)

–

4

(

n

–

n

+

1

)

⇒

a

n

=

3

(

2

n

–

1

)

–

4

⇒

a

n

=

6

n

–

3

–

4

⇒

a

n

=

6

n

–

7

Thus, the nth term of the

A

.

P

=

6

n

–

7.