Causal

Today, when i surfing around the internet, I saw this title

"World's Hardest Easy Geometry Problem"

Then I kicked in

http://thinkzone.wlonk.com/MathFun/Triangle.htm

 this website and saw this problem 

I have 4 HW today, so after i tried to use 10 mins to solve this, i failed. And now i think i should deal it

tomorrow. So, everybody interests in this problem can do it by yourself! Perhaps tomorrow i will give my 

answer! Basically, I haven't solved this question for a long time.