It is known that m.n is the midpoint of vector AB and vector CD of any two line segments, and the vector Mn = 1 / 2 (vector AD + vector BC) is proved
prove:
Because the vector am + Mn + Nd + Da = 0
Vector BM + Mn + NC + CB = 0
The sum of the two formulas is as follows:
2 vector Mn + (am + BM) + (Nd + NC) + (DA + CB) = 0
And m and N are the midpoint, so the vector am + BM = 0, Nd + NC = 0
So, 2 vector Mn = - (vector Da + CB)
Namely: vector Mn = 1 / 2 (vector AD + BC)
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