Question

Find the 20th 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 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