I was helping my daughters with some school projects in graphing, and I thought that it would be good  to document and share our discussion. This blog will look at solving the equations for plots using Desmos, Google Docs and Excel.

Desmos

Desmos (https://www.desmos.com/calculator) is great online free graphing package that is used in many school systems. Desmos has a lot of options to simulate, tweek and view data.

To add a table of data, use the “+” button and select table.

Once the data table has been entered an f(x) expression can be linked to the data. In the example below a linear expression was used. It’s important to note, two things:

• • The subscript must match. So if the table uses: y₂  x₂ then the formula needs to use the same.
  • A ~ (tilda) is used instead of an = (equals) sign.

 

If the formula matches up with the table a plot will be drawn and the slope, intercept and r-squared (goodnes of fit) values will be shown.

We found that for simple first order (straight line curves) Desmos worked really well, however for polynomials and other more advanced equations it was a little awkward.

Google Docs

Our school board uses Google Classroom which is an online suite of tools that enables kids to do Microsoft Excel, Word and Powerpoint in a free web based environment.

The Sheets options (https://docs.google.com/spreadsheets) of Google Docs works very much like Excel. To do some charting, enter a table of data and use the “chart” button to present the desired plot.

In the “Customize” options of the chart, under Series, a trend line can be added with an equation and a R-squared (fitness of curve) text.

It is also possible to use the SLOPE, INTERCEPT and RSQ formulas show the results in a cell.

The regression type supports functions such as log, exponential, and polynomial. For the example below we got the equation for a 2nd order polynomial.

Note: Sheets can import and export to and from Excel.

Excel

Different versions of Excel (and LibreOffice) will have a slightly different way to get the stats on a curve. For our work we used Excel from Office 2016.

In the Chart Elements, under Trend Line, the more Options items will offer features that are almost identical to Google Sheets.

A type of trend line can be selected and the solved equation and R-squared value can be shown on the plot.

Advanced equations like higher order polynomials can also be used.

Excel (and LibreOffice) support function calls for : SLOPE, INTERCEPT and RSQ.

 

Summary

Desmos is an excellent package for kids to play with and understand the different plot types, but it probably isn’t the best tool for doing curve fits of test data for projects.

Excel and Google Sheets are excellent for most charting and plot statistical projects.