Question

Find the nth term of the A.P. 5, 11, 17, 23, ......... . Using it, find its (i) 11th term (ii) 21st term.

Answer 1

Here $$a = 5$$ and $$d = 11 - 5 = 6$$. 

nth term: $$T_n = 5 + (n - 1) \times 6 = 6n - 1$$. 

Therefore $$T_{11} = 6 \times 11 - 1 = 65$$ and $$T_{21} = 6 \times 21 - 1 = 125$$. 

So nth term = 6n – 1, 11th term = 65, 21st term = 125.