4 1 Extreme Values of Functions The textbook

4. 1 Extreme Values of Functions

The textbook gives the following example at the start of chapter 4: The mileage of a certain car can be approximated by: At what speed should you drive the car to obtain the best gas mileage? Of course, this problem isn’t entirely realistic, since it is unlikely that you would have an equation like this for your car.

We can graph this on the calculator… Notice that at the top of the curve, the tangent has a slope of zero. Traditionally, this fact has been used both as an aid to graphing by hand as a method to find maximum (and minimum) values of functions.

Find any maximum and/or minimum points for the graph of: Notice that in two critical places, the tangent has a slope of zero. In order to locate these points precisely, we need to find the values of x for which

Find any maximum and/or minimum points for the graph of: Without seeing the graph, how could we tell which of these two points is the maximum and which is the minimum? In order to locate these points precisely, we need to find the values of x for which

maximum Remember this graph from when we first discussed derivatives? minimum f (x) f ´(x) > 0 f ´(x) < 0 f ´(x) > 0 increasing decreasing increasing f ´(x)

Find any maximum and/or minimum points for the graph of: + max So let’s test the intervals: + min Important note: The above number line without an explanation will not be considered sufficient justification on the AP Exam

Find any maximum and/or minimum points for the graph of: Now we have a way of finding maxima and minima. But we still need to better classify these points…

Terms to remember for you note-takers: Absolute maximum Also called a global maximum Local maximum Also called a relative maximum Note that an absolute max/min is already a local max/min Local minimum Also called a relative minimum Notice that local extremes in the interior of the function occur where is zero or is undefined.

Terms to remember for you note-takers: Extreme Value= any maximum or minimum value of a function Absolute maximum = global maximum Absolute minimum = global minimum Relative maximum = local maximum Relative minimum = local minimum Absolute or Global Extreme Values Relative or Local Extreme Values Even though the graphing calculator and the computer can help us find maximum and minimum values of functions, having the wrong window setting could cause us to miss a max or min of a function. However, the method we just used would find any max or min regardless of where we are looking on a graph.

Local Extreme Values: If a function f has a local maximum value or a local minimum value at an interior point c of its domain, and if exists at c, then Critical Point: A point in the domain of a function f at which or does not exist is a critical point of f. Note: Maximum and minimum points in the interior of a function always occur at critical points, but critical points are not always maximum or minimum values.

Critical points are not always extremes! (not an extreme)

(not an extreme)

Finding Maximums and Minimums Analytically: 1 Find the derivative of the function, and determine where the derivative is zero or undefined. These are the critical points. 2 Find the value of the function at each critical point. 3 Find values or slopes for points between the critical points to determine if the critical points are maximums or minimums. 4 For closed intervals, check the end points as well.

Extreme values can be in the interior or the end points of a function. No Absolute Maximum Absolute Minimum

Absolute Maximum Absolute Minimum

Absolute Maximum No Minimum

No Maximum No Minimum

Extreme Value Theorem: If f is continuous over a closed interval, then f has a maximum and minimum value over that interval. Maximum & minimum at interior points Maximum & minimum at endpoints Maximum at interior point, minimum at endpoint

FINDING ABSOLUTE EXTREMA Find the absolute maximum and minimum values of on the interval. There are no values of x that will make the first derivative equal to zero. The first derivative is undefined at x=0, so (0, 0) is a critical point. Because the function is defined over a closed interval, we also must check the endpoints.

At: To determine if this critical point is actually a maximum or minimum, we try points on either side, without passing other critical points. Since 0<1, this must be at least a local minimum, and possibly a global minimum. At:

At: To determine if this critical point is Absoluteor minimum, we actually a maximum try points on minimum: either side, without passing other critical points. Absolute maximum: Since 0<1, this must be at least a local minimum, and possibly a global minimum. At:

Absolute maximum (3, 2. 08) Absolute minimum (0, 0)

Now you are ready to handle Assignment 4. 1…