I thought that I have good background Mathematics and that this should be an easy problem in Geometry. Just the opposite, this proved wrong. I'm totally stumped. Please help me to solve the problem.

binary search? what is the relationship between this problem and binary seach? isnt it totally math? please give me enlightment..
i havent solved this problem, and i'm very weak in math.
thanks before...

Sorry. I am not correct. My mind was somewhere near 90 degrees.
Only 7th formula is not correct. r/c = c/r1 = z*z*d
d = sin(90+alfa+beta). I have to find what it is.

Thanks to all. After all finding an equation and solving it through binary search was enough. However a mathematician always tries to find some nice looking formula which maybe is not possible in this problem (our mistake).

Hi BiK. You are right. I know how to solve it with binary search. But I want to solve it matematically. And it is possible because l depends on only x,y and c. I just have to find dependence between them.

I've found an idea:
solve sqrt(x^2-l^2)*sqrt(y^2-l^2)/(sqrt(x^2-l^2)+sqrt(y^2-l^2))-c=0
and I've written an program for solving this
but the online judge told me wrong answer
Who can tell me how to debug this? Can I see the test datas?