Proof: Draw an auxiliary line through the point A and parallel to segment BC. Next, extent segments CF and BE until they intersect the parallel line and label those points H and G, respectively.
Now, the following triangles are similar by Angle-Angle Similarity because in each case one pair of angles are vertical angles (therefore congruent) and the other pair are alternate interior angles formed with parallel lines (therefore congruent).
Since similar triangles, there are proportional sides (notice the proportions are set up to have the sides needed for the prove statement).
Now, I will multiply all the ratios on the left together and all the ratios on the right together.
Multiply both sides by GA/AH. Therefore,