Given a_n = 3 + 4n

Then a₁ = 3 + 4 × = 3 + =

a₂ = 3 + 4 × = 3 + =

a₃ = 3 + 4 × = 3 + =

a₄ = 3 + 4 × = 3 + =

Now the pattern is 7, 11, 15, ……

where a = a₁ = ; a₂ = 1; a₃ = , ….. and

a₂ – a₁ = – = ;

a₃ – a₂ = – = ;

Here d =

Hence a₁, a₂, ….., a_n ….. forms an A.P.

= × =