Question

10.If the nth term of an A.P is
given by an= 3n, then 5th term
of the A.P is
O a)15
O b) 729
O c)243
O d) 81​

Answer 1

Question:-

If the nth term of an AP is given by aₙ= 3n , then 5th term of the AP is

Solution:-

We have

aₙ = 3n

=>when n = 1

a₁ = 3 × 1 = 3

=>when n = 2

a₂= 3 × 2 = 6

=>when n =3

a₃ = 3 × 3 = 9

=>when n = 4

a₄ = 3 × 4 = 12

Now have series:- 3 , 6 , 9 , 12 ,.........

So

First term ( a ) = 3 , common difference ( d ) = 6 - 3 = 3

We have find 5th term

so n = 5

Formula

Formula Tₙ = a + ( n - 1 )d

=> 3 + ( 5 - 1 ) × 3

=> 3 + 4 × 3

=> 3 + 12

=> 15

So 5th term of AP is 15 option a is correct