Question

Decide whether the following sequence is an A.P., if so find the 20^th term of the progression:

–12, –5, 2, 9, 16, 23, 30, ..............

Answer 1

Here a = t₁ = first term = – 12, t₂ = – 5,

Common difference = d = t₂ – t₁

d = – 5 – (– 12)

= – 5 + 12

∴ d = 7

We know that, t_n = a + (n – 1)d

Here, n = 20, a = – 12, d = 7

∴ t₂₀ = – 12 + (20 – 1)7

= – 12 + 133

t₂₀ = 121

∴ 20^th term of the progression is 121.