def sqrt_divide(n,epsilon=1e-9):
    '''
    二分法逼近求平方根
    :param n:
    :param epsilon:
    :return:
    '''
    low=0
    high=n
    while low<high:
        mid=low+(high-low)/2
        if abs(mid*mid-n)<epsilon:
            return mid
        else:
            if mid<n/mid:
                low=mid
            else:
                high=mid