Question 1040566
Draw it.  The lines between the two Quadrant III points and the other two points should have the same slope and be parallel.
The slope is -1/2 between (-8,-5) and (-6,-6).  It is -1/2 for the other two points, too.
Between (-6,-6) and (7.2) slope is 8/13.  That should be the same between (5,3) and (-8.-5).  It is.
The sides should be equal length.  The distance between the third quadrant points is sqrt(1^2+2^2)  The distance between the two first quadrant points is (1^2+2^2).  For the longer sides, (-6,-6) and (7,2), it is sqrt (169+64), and for the other two (5,3) and (-8,-5), it is sqrt (64+169).
For the angles, one may show that the diagonals intersect at their midpoint.  Then the triangles formed would be congruent on the basis of SAS (the angles being vertical angles).
Diagonal from (-6,-6) to (5,3) has slope 9/11 and its equation is y-3=(9/11)(x-5)
That is y=(9/11)x-(12/11)
The other diagonal is from (-8,-5) to (7,2).  Its slope is (7/15) and function is y-2=(7/15)(x-7). That is
y=(7/15)x-19/15
The intersection of the two diagonals is solving this system.
11y-9x=-12
15y-7x=-19
77y-63x=-84
-135y+63x=+171
-58y=87; y=-3/2
-16.5-9x=-12
-9x=4.5; x=-0.5
Check into second.  -22.5+3.5=-19
intersect at (-0.5,-1.5)
The midpoint of the first diagonal is (-.5,-1.5)
The midpoint of the second diagonal is (-.5,-1.5)
The angles between the half diagonals are equal.  
SAS and the angles are equal.