Y by
In the parallelogram
is the midpoint of
and
the orthogonal projection of
on
. Prove that the triangle
is isosceles.

![$[ABCD], E$](http://latex.artofproblemsolving.com/e/9/f/e9f553aa610bca2c2cc1c33e728fee5bab6bbd9a.png)
![$[AD]$](http://latex.artofproblemsolving.com/0/f/3/0f3e4c424371b27673db323ced8ef0777940c0d4.png)


![$[CE]$](http://latex.artofproblemsolving.com/e/a/8/ea8eadb930f32cceb220dee99277c24b202fb80c.png)
![$[ABF]$](http://latex.artofproblemsolving.com/b/f/1/bf11edc79e86030d295b579e931ae40a83a6d815.png)

Free webinar 4/3 about Learning with AoPS: Perspectives from a Parent, Math Camp Instructor, and University Professor.
Something appears to not have loaded correctly.