Question

Find:
(i) the 20^th  term of the AP 9,13,17,21,..........

Answer 1

The given AP is 9,13,17,21,..........
First term, a = 9
Common difference, d =13 - 9 = 4
n^th  n term of the AP, a_n = a + (n-1) d= 9 + (n-1)  × 4
∴ 20^th  term of the AP,a₂₀ = 9 +(20 -1)× 4=9+76=85