The problem as stated cannot be done. You cannot prove something that in general is not true. Now if MATH were actually a rhombus, that is another story altogether.
Here's the proof that your Prove statement is false in general.
Construct two parallelograms that are on top of one another: and such that is significantly greater than . Construct the diagonals and .
Since angle is congruent to but the alleged half-angles and are clearly of different measures, the two diagonals cannot be bisectors.
