Question

Show that the progression 11, 13, 15, 17, 19, ......... is an A.P. Write down its (i) first term (ii) common difference (iii) 20th term.

Answer 1

Common difference is constant:

$$13 - 11 = 15 - 13 = 17 - 15 = 19 - 17 = 2$$. 

Hence it is an A.P.

First term $$a = 11$$, common difference $$d = 2$$. 

20th term: $$T_{20} = a + (20 - 1)d$$

$$= 11 + 19\times 2$$

$$= 49$$

So first term = 11, common difference = 2, 20th term = 49.