Theorem 6.4 Triangle Proportionality Theorem
If a line is parallel to one side of a triangle and intersects the other sides, it divides the two sides proportionally.
Theorem 6.5 Converse of the Triangle Proportionality Theorem
If a line divides two sides of a triangle proportionally, then it is parallel to the third side.
Source: McDougal Littel High School Geometry
"How to prove and use properties of triangle midsegments. Yeah, it's that important."
Source: http://tylertarver.com
If three or more parallel lines intersect two transversals, then they cut off the transversals proportionally.
In the figure shown, if 
, then 
and 
Example found at the bottom of this page: http://hotmath.com/hotmath_help/topics/parallel-lines-and-transversals.html
