Answer
The diagonals are congruent.
Work Step by Step
The Length of $\overline{EG}$ can be found as:
$d =\sqrt {(x_2-x_1)^2+(y_2-y_1)^2}=\sqrt {(-a-b)^2+(0-c)^2}=\sqrt {a^2+b^2+c^2}$
The Length of $\overline{FH}$ can be found as:
$d =\sqrt {(x_2-x_1)^2+(y_2-y_1)^2}=\sqrt {(-b-a)^2+(c-0)^2}=\sqrt {a^2+b^2+c^2}$
We can see that the diagonals are congruent because their respective lengths are equal.
