Question

Find the second term and n^th term of an A.P. whose 6^th term is 12 and 8^th term is 22.

Answer 1

In the given problem, we are given 6^th and 8^th term of an A.P.

We need to find the 2^nd and n^th term

Here, let us take the first term as a and the common difference as d

We are given,

`a_6 = 12`

`a_8 = 22`

Now we will find `a_6` and `a_8` using the formula `a_n = a + (n - 1)d`

So

`a_6 = a + (6 -1)d`

12 = a + 5d  ....(1)

Also

`a_8 = a + (8 -1)d`

22 = a + 7d ....(2)

So to solve for a and d

On subtracting (1) from (2), we get

22 - 12 = (a + 7d) - (a + 5d)

10 = a + 7d - a - 5d

10 = 2d

`d = 10/2`

d = 5    ....(3)

Substituting (3) in (1) we get

12 = a + 5(5)

a = 12 - 25

a = -13

Thus

a= -13

d = 5

So, for the 2 nd term (n = 2)

`a_2 = -13 + (2 - 1)5`

= -13 + (1)5

= -13 + 5

= -8

For the nth term

`a_n = -13 + (n - 1)5`

= -13 + 5n - 5

= -18 + 5n

Therefore `a_2 = -8, a_n = 5n - 18`