Problem
Prove that the congruence equation $ax^2 + bx + c \equiv 0 \pmod{m}$, with $(2a, m) = 1$ is equivalent to a congruence of the form $x^2 \equiv r \pmod{m}$.
I really have no idea where to start. Is there a theorem which relates to this problem? What do we have to show? A hint would be sufficient.
Thanks,