You can put this solution on YOUR website!
let ABCD be your parallelogram
A is bottom left
B is top left
C is top right
D is bottom right.
let ABCD lean to the right so that point B is slightly to the right of point A.
all you need is a little tilt to show that it's not a rectangle.
draw diagonals AC and BD.
AC is the long diagonal and BD is the short diagonal.
BC congruent to AD (opposite sides of a parallelogram are congruent)
AC and BD are diagonals of the parallelogram.
they are also transversals that intersect two parallel lines (BC and AD).
angle ACB congruent to angle CAD (opposite internal angles caused by the intersection of a transversal with two parallel lines are congruent).
likewise, angle DBC congruent to angle BDA.
you have triangles AED congruent to triangle CEB (ASA)
the ASA is formed by:
side BC congruent to side AD
angle ACB congruent to angle CAD
angle DBC congruent to angle BDA.
CE is congruent to AE (corresponding parts of congruent triangles are congruent)
BE is congruent to DE (same reason).
a sketch of the parallelogram can be found at this website:
look for 169616 parallelogram
shouldn't be too hard to find.
it's the only one there.