Question 1073222
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I will try to guess what you want:


<pre>
     <U>Theorem</U>

     If a straight line connecting two sides of a triangle is parallel to its third side  then the straight line divides these sides proportionally. 
</pre>

If my guess is right, then see the lesson

&nbsp;&nbsp;&nbsp;&nbsp;-<A HREF=http://www.algebra.com/algebra/homework/Parallelograms/Straight-line-in-a-triangle-parallel-to-its-side-cuts-off-proportional-segments-in-two-other-sides.lesson>Straight line in a triangle parallel to its side cuts off proportional segments in two other sides</A>

in this site.



Also, &nbsp;you have this free of charge online textbook on Geometry

&nbsp;&nbsp;&nbsp;&nbsp;<A HREF=https://www.algebra.com/algebra/homework/Triangles/GEOMETRY-your-online-textbook.lesson>GEOMETRY - YOUR ONLINE TEXTBOOK</A> 

in this site.


The referred lesson is the part if this textbook under the topic 
"<U>Parallel lines cutting off transverse lines in congruent or proportional segments</U>".