® A function f is said to be

® A function f is said to be (a) increasing on an interval ( a , b ) if x < x in ( a , b ) ⇒ f ( x ) < f ( x ) for all x , x ∈ ( a , b ). Alternatively, if f ′ ( x ) ≥ for each x in ( a , b ) (b) decreasing on ( a , b ) if x < x in ( a , b ) ⇒ f ( x ) > f ( x ) for all x , x ∈ ( a , b ). (c) constant in ( a , b ), if f ( x ) = c for all x ∈ ( a , b ), where c is a constant. ® A point c in the domain of a function f at which either f ′ ( c ) = or f is not differentiable is called a critical point of f .