Question

(i) The third and the seventh terms of an A.P. are 20 and 36 respectively. Find the first

term and the common difference,​

Answer 1

The first term is 12. The common difference is 4.

Explanation:

`a_n = a_1 + d(n - 1)`

The difference between the third and seventh terms is

36 - 20 = 16

The 7th term is the 4th term after the 3rd term, so the common difference is

16/4 = 4

`a_3 = a_1 + 4(3 - 1)`

`20 = a_1 + 4(3 - 1)`

`20 = a_1 + 8`

`a_1 = 12`

Answer: The first term is 12. The common difference is 4.