perps

draw two lines, AB and AC
with any point, D, 'between' them

drop perpendiculars from D to AB (at F) and from D to AC (at E)

join E to F (the feet of these perpendiculars)

then create a perpendicular from A to EF (meeting EF at G)


possibly set this up (e.g. with GeoGebra)

establish, by measuring and dragging D around
that angle GAE = angle FAD

try to prove it

can students find another angle the same as these?