Question 1023311
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ABC is an equilateral triangle with AB=20CM a second equilateral triangle DEF is constructed by joining the midpoints of the sides of the first triangle ABC
how do I determine the length of DE
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The length of he straight segment connecting midpoints of the two sides of a triangle is half of the length 
of the third side of the triangle.


See the lesson <A HREF=http://www.algebra.com/algebra/homework/Triangles/The-line-segment-joining-the-midpoints-of-two-sides-of-a-triangle.lesson>The line segment joining the midpoints of two sides of a triangle</A> in this site.


Thus |DE| = {{{1/2}}}.|AB| = 10 cm.