Plotting a quadratic with Excel 2003

Rod Rodrigues 2003

Let’s suppose you want to graph the function  using Excel. A little preliminary work tells you that the x-intercepts are  x=2 and x=4   since in factored form we have . Knowing that I want the graph to stretch from x = 2 to x = 4 at least, I decide that I would like to graph, say from x = 0 to x = 5. Next, decide how many values I want to graph. In this case, perhaps I want to graph for values of x going from 0 to 5 in increments of 0.25. The basic decisions are now made, so it is time to fire up Excel to let it do all the heavy work.

Column A will be for the x-values.

1. In cell A4, enter the number 0.
2. Move to cell A5, and enter the formula     =A4+0.25.  The number .25 will pop in for you:
   
   
   
3. Click on cell A5. Then move the cursor so it is over the lower right hand corner of the cell, where you see the “corner”
   
   
   The cursor becomes a plus sign
   
   
4. Click and drag the mouse down column A as far as you want. This will fill column A with a range of values for x. Since we want to go from 0 to 5, we need to stretch far enough so that we generate that range of x values. In this case it means we have to stretch it down to cell A24.
   
   
   
5. Now that we have all the x-values, we need to generate the y-values. So move to cell B4, next to the first x-value. We need .
   We type into cell B4 the formula to get this from cell A4 as follows:   =A4^2-6*A4+8
   
   
   
   
   
6. Now we need to copy THAT down column B. Click on the lower right-hand corned, and stretch it down to match the A column.
   
   
   
   
7. This gives us a lot of values to plot, so the curve will be fairly smooth.
8. Next, highlight the values in column B that we want to graph:
   
   
   
   
9. With this column highlighted, choose from the menu system Insert/Chart. From the first Chart Wizard window, select the second scatter plot:
   
   
   and click Next.
10. On the next screen, the wizard will already know which values you want to  plot:
    
    
    You may notice that your graph is essentially already plotted. But wait, there’s more. the labels on the x-axis are wrong. Click on the Series Tab in this window.
    
    
    
    To the right of x-values, click on the right-hand edge.
    
    
    
    This will give you a little floating window
    
    
    While this is on the screen, click inside your spreadsheet and select the column of x-values.
    
    Excel will fill in the appropriate information for you. Close that little floating window. Your screen should then look like this:
    
    
    
    Notice that the x-values are specified and the y-values are specified.
    
    
11. Your next screen looks like this – the job is essentially done. Click Finish.
    
    
    
12. You now have a floating Chart in your spreadsheet – the graph of the data.
    
    
    
    
13. If you need to, you can highlight the entire thing – columns and chart - and copy it to the clipboard. Then you can paste it into a Word document.
    
    I hope this helps. Please note: you can play with aspects above to customize to your own preferences. There is more that you can do to (with) the graph. I will attach the finished spreadsheet so that you can load it and interact with it.