Kaba ha usato la sua tastiera per scrivere : >> Hi all, >> >> I need help with this problem: >> >> http://img180.imageshack.us/img180/8286/20080218181526nq7.gif >> >> The angle to find is ECD. >> >> The matter is solving it without trigonometric functions. >> With trigonometry or by drawing it you can see that the angle to find is >> 20° (sessagesimal) but I can't find it using a simple solution (properties >> of triangles, the parallel postulate and so on). >> >> Can you solve it? > > Interesting problem, couldn't solve it either. I get 4 unknowns but only 3 > linearly independent equations.
I'm not sure if an equation system is needed. I guess drawing a few parallels and looking for properties like angle bisector theorem, Thales' theorem, etc... should do the trick by showing two similar triangles.
Anyway, I don't have any hint, this is only my approach so it could also be wrong ;)