I think the tests for this problem are very simple!!!
Here is the solution, which gets AC: I just divide the [-R; R] into 10 (!!!! only 10 !!!!!) parts and for every X from those 10 (!!!) values I calculate two corresponding Y => I get 20 points => calculate the nearest piece for every point and output the one with the biggest piece.

Isn't it to simple???

i did what you said, but got WA,
i also divided the interval into 100 parts
also getting WA
could you explain clearly

I think, now the above solution is incorrect...

Of course this solution gets WA now. Admins added new tests...