The derivative of a function may be used to determine whether the function is increasing or decreasing on any intervals in its domain. If f′(x) > 0 at each point in an interval I, then the function is said to be increasing on I. f′(x) < 0 at each point in an interval I, then the function is said to be decreasing on I. Let y=f(x) be a differentiable function on an interval (a,b). If for any two points x1,x2∈(a,b) such that x1<x2, there holds the inequality f(x1)≤f(x2), the function is called increasing (or non-decreasing) in this interval.