Question 867139
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Hi
A(0,-1)
B(1,2), m = -3/-1 = 3
C(-4,7) m = -5/5 = -1
D(-5,4) m = 3/1 = 3
A(0,-1) m = 5/-5 = -1
If 
*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \overline{AB}\ \parallel\ \overline{CD}] and *[tex \LARGE \overline{DA}\ \parallel\ \overline{CB}] 
then ABCD is a parallelogram.
A(0,-1),
C(-4,7) Midpoint = ( -2, 3)
B(1,2), 
D(-5,4) Midpoint = ( -2, 3)
OR if
*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \overline{AC}] bisects *[tex \LARGE \overline{BD}] and *[tex \LARGE \overline{BD}] bisects *[tex \LARGE \overline{AC}]
then ABCD is a parallelogram.