def f(x):
    return -3*x**3+4*x+1
def trichotomie_min(f,a,b,n):
    e=10**(-n)
    while b-a>e:
        m=(b-a)/3
        c=a+m
        d=b-m
        if f(d)<=f(c):
            a=c
        else:
            b=d
    return (round(a,n),round(b,n))