1, 3, 6, 10, ..... (1 mark)

(i) 1, 3, 6, 10, ..... (1 mark)

Sol. t₁ = 1, t₂ = 3, t₃ = 6, t4 = 10

t₂ – t₁ = 3 – 1 = 2

t₃ – t₂ = 6 – 3 = 3

t₄ – t₃ = 10 – 6 = 4

Here, The difference between ANY two consecutive terms is not constant.

∴  The sequence is not an A.P.