Let’s see algebraic numbers countable by following example.
Set below can be said as algebraic number if all integers P_ 0... P_ t are not zero. That is,
P_ 0 X t + P_ 1 X t-1 +...+ P_ t-1 X + P_ 0 = 0.
If we want to prove that set of all algebraic numbers is countable, following procedure is used. Consider a set P_ 1 of algebraic numbers in such a way that P_ 0 X + P_ 1 = 0. It simply expresses the rational numbers, and therefore is countable. Let’s suppose that set P_ n, of algebraic numbers P_ 0 X t +...+ P_ n = 0, is countable. Then again suppose that set P_ n + 1, of algebraic numbers P_ 0 X t + 1 + P_ 1 X t +...+ P_ t + 1 = 0. Now select a fixed P_ 0 = P, then this subset of P_n+1 can be put in One-to-One Correspondence with P_n and therefore is countable.