Check the picture below.
well, it's noteworthy to say that when dropping a perpendicular line from a right angle in a right triangleto the hypotenuse, we'd end up with 3 similar triangles, a Large a Medium and a Small one, all three similar.
3a)
is the Small similar to the Large one? well, let's notice, they both have a 90° angle and also they share the purple one, similar triangles by AA.
3b)
are the Medium and the Large one similar? well, let's notice, just like before, they both have a 90° and they also share the green one, similarity by AA.
3c)
are the Small and Medium similar?
if Large ~ Medium
and
Large ~ Small
then
Medium ~ Small.