function c=Bisect(poly,X,Y)

a=0;
b=10;
N=37;
for i=1:N
    c=(a+b)/2;
    if fun(poly,X,Y,c)==0
        i=N;
    elseif sign(fun(poly,X,Y,c))*sign(fun(poly,X,Y,a))<0
        b=c;
    else
        a=c;
    end
end