Vector proof - four points in space

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SUMMARY

The discussion centers on a geometric proof involving four points A, B, C, and D in space, with M and N defined as the midpoints of segments AC and BD, respectively. The objective is to demonstrate that the equation AB + CB + CD = 4MN holds true. Participants express uncertainty about the problem's correctness, particularly when considering specific configurations like a square, where both midpoints M and N coincide at the center. A suggestion is made to include an additional segment AD for clarity in the equation.

PREREQUISITES
  • Understanding of vector geometry
  • Familiarity with midpoint calculations
  • Knowledge of geometric proofs
  • Basic algebraic manipulation skills
NEXT STEPS
  • Study vector geometry principles
  • Learn how to calculate midpoints in three-dimensional space
  • Explore geometric proof techniques
  • Investigate the properties of squares and their midpoints
USEFUL FOR

Students and educators in mathematics, particularly those focused on geometry and vector analysis, as well as anyone interested in developing proof-writing skills.

nc01
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The problem is: A, B, C, D are any four points in space. If M and N are the mid-points of AC and BD, show that AB + CB + CD = 4MN.

I'm not quite sure where to start. Could someone please help me?
 
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I'm not sure that the problem is correct. Suppose that A,B,C,D are the four corners of a square. In this case, M and N would both be the center of the square. This would make MN=0
 
welcome to pf!

hi nc01! welcome to pf! :smile:
nc01 said:
The problem is: A, B, C, D are any four points in space. If M and N are the mid-points of AC and BD, show that AB + CB + CD = 4MN.

?? :confused:

i think you need an AD in there …

AB + AD + CB + CD = 4MN :wink:
 

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