Question 473073
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Hi,
Note: D = {{{sqrt ((x[1]-x[2])^2+(y[1]-y[2])^2))}}}
1) (5,-8), 
   (0,0)    D ={{{sqrt( (5-0)^2 + (-8-0)^2) = sqrt(89)}}}

2) (a,b)  
  (-a,-b)   D ={{{sqrt( (a+a)^2 + (b+b)^2) = sqrt(4a^2 + 4b^2)}}}