def fx(x):
    return x**4-3*x+1


def erfen(x1,x2,err):
    while abs(x2-x1) >= err:
        x = (x1+x2)/2
        if fx(x) * fx(x1) < 0:
            x2 = x
        else:
            x1 = x
    return (x1+x2)/2


if __name__ == "__main__":
    x1 = 0.3
    x2 = 0.4
    root = erfen(x1, x2, 0.5e-5)
    print(f"解为: {root}")