def lagrange(f,a,b,epsilone=0.1):
    k = 0
    u,v = [a],[b]
    x = [(u[k]*f(v[k])-v[k]*f(u[k]))/(f(v[k])-f(u[k]))]
    while (v[k]-u[k]>epsilone) or (abs(f(x[k]))>epsilone):
        if f(u[k])*f(x[k])<0:
            u.append(u[k])
            v.append(x[k])
        else:
            u.append(x[k])
            v.append(v[k])
        x.append((u[k+1]*f(v[k+1])-v[k+1]*f(u[k+1]))/(f(v[k+1])-f(u[k+1])))
        k = k + 1
    return x[-1]