Given a particular function, we are often interested in determining the largest and smallest values of the function. This information is important in creating accurate graphs. Finding the maximum and minimum values of a function also has practical significance because we can use this method to solve optimization problems, such as maximizing profit, minimizing the amount of material used in manufacturing an aluminum can, or finding the maximum height a rocket can reach.
The mean value theorem states that for a given planar arc between two endpoints, there is at least one point at which the tangent to the arc is parallel to the secant through its endpoints. This theorem is used to prove statements about a function on an interval starting from local hypotheses about derivatives at points of the interval.
We know that the sign of the derivative tells us whether a function is increasing or decreasing; for example, when f′(x)>0, f(x) is increasing. The sign of the second derivative f′′(x) tells us whether f′ is increasing or decreasing; we have seen that if f′ is zero and increasing at a point then there is a local minimum at the point, and if f′ is zero and decreasing at a point then there is a local maximum at the point. We extracted information about f from information about f′′.
In many areas of pure and applied mathematics, we are interested in finding solutions to an equation of the form f(x)=0. For most functions, however, it is difficult—if not impossible—to calculate their zeroes explicitly. In this section, we take a look at a technique that provides a very efficient way of approximating the zeroes of functions. This technique makes use of tangent line approximations and is behind the method used often by calculators and computers to find zeroes.