0 0
0 1000
1 0
YES

0 0
1 1000
1 0
YES

0 0
1 1000
2 0
YES

Real thanks, Sergey.
I had WA3. When I test my program with your tests, I get wrong answer on the second test. My mistake was in comparing the angle ACB with 90 degrees. There was (in C++):
if (angle==pi/2.0)...
but the right text would be:
if (fabs(angle-pi/2.0)<=1e-11)...

When I fixed the problem I got AC.

Never forget to use EPS when compare real numbers. Without it, result of the work of your program is almost unpredictable

0<=|x|,|y|<=100
But tests are useful :)

Edited by author 18.05.2009 12:28

If 1000 insted of 100 prevents your program from passing the tests, then your program is really horrible =)
P.S. I've written 1000 instead of 100 as a very corner cases specially to test possible error instability.

I have known that.