Question 894518
1) You could show opposites sides are equal length
2) You could show that angles are 90 degrees ie sides are perpendicular
3) You could show opposite sides are parallel.
I will show 2 and 3
 P (0, -4), Q (6,2)
y= 1x-4 pq 
, R (3,5) and S (-3, -1) 
y= 1x+2 rs
pq and rs are parallel
      r
s    
         q
   p    

y= -1x+8 r q

 0, -4,-3, -1 
y= -1x-4 p s
from the slope we can see that 
pq and rs are parallel
rq and ps are parallel

pq and ps are  perpendicular
rq and pq are  perpendicular
rs and ps are  perpendicular
rs and rq are  perpendicular
we have two sets of parallel lines and 4 right angles