If a₁, a₂, a₃, …… are in A.P, then

a₁ ± k , a₂ ± k , a₃ ± k , a₄ ± k, ... are also in A.P.

a₁, a₂, a₃, ...... are also in A.P.

i.e., “If each term of an A.P is added/ multiplied / divided by a number, the resulting terms also form an A.P” and fixed term is subtracted from each term of an A.P, then the resulting terms also form an A.P.