Math 174, Spring 2004 Graphing Functions

Plotting Points Need to produce graphs that are well-formatted as well as informative We can have Excel do this for us Excel needs many points to graph accurately Many is a relative term

Example 1 We have a function Let’s have Excel graph this function over [0,4] We need values of f(x) to do this – how can we get them?

Determining Points for Graph Want a large enough number of points – arbitrary number If graph is not pretty, you didn’t choose enough The text chooses 501 points so it evenly divides the interval where x 0 =0 and x 500 =4 Note: We have 501 points since we start at x 0 We now have to determine what the distance between any 2 adjacent points (4-0)/500 = The distance between any 2 adjacent points is 0.008

Graph Examples.xls Now that we have the number of points we need + the distance between any 2 adjacent points, we need to have Excel graph the function Need to use the IF function to generate y-values IF(statement, rule 1, rule 2) If the statement is true, IF uses rule 1; else it uses rule 2 We will use rule 1 to be and 0 to be rule 2 Our statement will be Let’s look at Graph Examples.xls to see how Excel graphed the function using our pointsGraph Examples.xls

Graphing Once we have the values of f(x) that we need, we can have Excel generate a graph for us Go to Chart Wizard and choose XY Scatter plot, with no markers We must enter our data range for the y- values and then change the series to show the x-values Let’s try

Graphing Several Functions You can also have Excel graph multiple functions on one set of axes Doing so helps us understand the connections between the quantities that are represented Think back to Project 1: Need a Demand curve, Revenue curve, Cost curve, and Profit curve To do this, you will follow all the previous steps that you did to graph one function

Graphing Several Functions You need to determine how many points you need for each function you want to graph Also, you need to determine the distance between any 2 adjacent points Have Excel determine the y-values for each x-value by using the IF function

Example 2 If your functions were and you wanted Excel to graph them over [0,2000], what would your IF statements be for each? Let’s see what the graphs look like

Grahping Utility To create your own graphs can be time consuming (although very valuable) A graphing utility, Graphing.xls, has been provided to you in the course filesGraphing.xls Open up the file and follow the directions in the blue box Note: This file contains macros which you need to enable – if you cannot produce a graph, you may not have enabled the macros A backup, Graphing BU.xls has also been provided (just in case)

Graphing Macro To make sure your macro runs, 1. Set your security at medium (prompt) or low (automatic) to enable your macro 2. Assign your macro View Graph toolbar Right click on toolbar and left click on customize (ignore window that comes up) Right click on toolbar again and left click on assign macro Highlight Graph, hit ok, and close window Your macro is now assigned

Practice You should practice working with the graphing utility, Graphing.xls Use example functions that have been given in the text You know what these graphs look like There are also exercises in the text that you can try You should know what the graphing utility is doing Know why you are entering specific items into each cell