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.Intervals of increasing, decreasing or constant ALWAYS pertain to x-values. Do NOT read numbers off the y-axis. Stay on the x-axis for these intervals! Intervals of Increasing/Decreasing/Constant: Interval notation is a popular notation for stating which sections of a graph are increasing, decreasing or constant.A function f(x) increases on an interval I if f(b) ≥ f(a) for all b > a, where a,b in I. If f(b) > f(a) for all b>a, the function is said to be strictly increasing.The slope and y-intercept values indicate characteristics of the relationship between the two variables x and y. The slope indicates the rate of change in y per unit change in x. The y-intercept indicates the y-value when the x-value is 0.
