Answer
For parallelograms, opposite sides have equal lengths.
Work Step by Step
We place the parallelogram at the origin. We call its coordinates:
$A: 0,0 \\ B: b,c \\ C: a+b, c \\ D: a, 0$
Thus, we compare the lengths of opposite sides:
$l_1= a $
$l_2=a+b-b =a$
$l_3 = \sqrt{c^2 + b^2}$
$l_4 = \sqrt{b^2 +c^2}$
We see that the lengths of opposite sides are equal.
