Find the A.P. whose nth term is 7 - 3n. Also find the 20th term.

Given, a_n = 7 - 3n     (Eq 1)

Putting n = 1, 2, 3, 4, …. in (Eq 1), we get

a₁ = 7 - 3 × 1 = 7 - 3 = 4,   a₂ = 7 - 3 × 2 = 7 - 6 = 1
a₃ = 7 - 3 × 3 = 7 - 9 = -2,   a₄ = 7 - 3 × 4 = 7 - 12 = -5, …

∴ Series = 4, 1, -2, -5 …..

Putting n = 20, for 20th term we get,

a₂₀ = 7 - 3 × 20 = 7 - 60 = -53.

Hence, the A.P. is 4, 1, -2, -5 ….. and the 20th term is -53.