function c=radicebisezione1(x)
if x<0
    disp('non accettabile')
    return
end
if x<=1
    a=x;
    b=1;
else 
    a=1;
    b=x;
end
e=0.0001;
fa=a*a-x;
fb=b*b-x;
c=(b+a)/2;
while b-a>=e
    c=(b+a)/2;
    fa=a*a-x;
    fc=c*c-x;
    if fa*fc<=0
        b=c;
    else
        a=c;
    end
end