Question 1012206
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the median of a trapezoid to each base and its lenght is one half the sum of the lenghts of the bases
to prove the theorem 
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See the lesson <A HREF=http://www.algebra.com/algebra/homework/Polygons/Trapesoids-and-their-mid-lines.lesson>Trapezoids and their mid-lines</A> in this site.
The Theorem and the proof are there.


One note: this line is called the mid-line</U> of a trapezoid, not the median.