  Based on the MRDP theorem, we introduce the ideas of the proof equation of a
formula and universal proof equation of Peano Arithmetic (PA); and then,
combining universal proof equation and G\"odel's Second Incompleteness Theorem,
it is proved that, if PA is consistent, then for every axiom and every theorem
of PA, we can construct a corresponding undecidable proposition with
Diophantine form. Finally, we present an approach that transforms seeking a
proof of a mathematical (set theoretical, number theoretical, algebraic,
geometrical, topological, etc) proposition into solving a Diophantine equation.
