Proportional Sides and Equal Angles: Exploring Similar Triangles in Geometry

[dekoi]

Oddly enough, i forget my geometry laws two days before the test.

If ABCD is a parallelogram where x and y are on the midpoints of AD and BC. Prove that BX and DY are parallel. I understand one would have to prove that corresponding angles are equal. thus, AHX would equal CMY, and ADM would equal BHC.

My question is: if a large triangle and a smaller triangle have proportional sides (e.g. 1/2), would the angles be proven equal?

 

[HallsofIvy]

Hey, you're not supposed to forget until AFTER the test!


Yes, if two triangles have sides in proportion, then they are "similar" triangles and have the same angles.

 

[dekoi]

Thank you HallsofIvy for reminding me about the similar triangles, as well as to forget everything i know after the test. :)