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| Question 212913:  if b is the mid point of ac and c is the mid point of bd, where a,b,c,d lie on a straight line, say why ab=cd?
 Answer by HyperBrain(694)
      (Show Source): 
You can put this solution on YOUR website! Since, b is the midpoint of ac then a, b, and c are collinear (the points lie on the same line) Since, c is the midpoint of bd then b, c, and d are collinear as well.
 So, a, b, c, and d are collinear.
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 Since b is the midpoint of ac, then ab=bc
 Since c is the midpoint of bd, bc=cd.
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 Now, since ab=bc and bc=cd, then
 ab=cd
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