Other Demostrative Perspective of How to See Dirichlet’s Theorem

The Dirichlet’s theorem (1837), initially guessed by Gauss, is a result of analytic number theory. Dirichlet, demonstrated that:
For any two positive coprime integers and , there are infinite primes of the form a+bn, where n is a non-negative integer ( n = 1, 2,… ). In other words, there are infinite primes which are congruent to mod b. The numbers of the form a+bn is an arithmetic progression.
Actually, Dirichlet checks a result somewhat more interesting than the previous claim, since he demonstrated that:

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Which implies that there are infinite primes, p Untitled.png a mod b.
The proof of the theorem uses the properties of certain Dirichlet L-functions and some results on arithmetic of complex numbers, and it is sufficiently complex that some texts about numbers theory excluded it. Here is a simple proof by reductio ad absurdum which does not require extensive mathematical knowledge.