Final Answer:
The least integer

Explanation:
In order to find the least integer n for which f(x) is positive for each function, we need to consider the critical points where
or is undefined. Let's analyze each function:

is positive when x is in the open interval (1
is the smallest integer satisfying this condition.
(c) Function
) is positive when x lies in the open interval ( (0 1) \). Therefore
ensures positivity for

(d) Function \( f_d(x) \) is positive when
. Thus
is the least integer for which
is positive.
In summary, for each function, the critical points are considered, and
is chosen as the least integer that ensures positivity in the respective intervals. This solution simplifies the analysis and provides a clear and concise answer to the given question.