Prove that there are infinitely many primes of the form $5k+3$
I known this is Dirichlet's Theorem Special case, but I want to find a similar following elementary proof:
1:there are infinitely many primes of the form $8k+3$, consider $x^2+2\equiv 0\pmod p$
2: there are infinitely many primes of the form $5k+4$, consider $x^2-5\equiv 0\pmod p$
3: there are infinitely many primes of the form $7k+6$, consider $x^3+x^2-2x-1\equiv 0\pmod p$