Graphing Inequalities

Thinking about resources to show students how to graph linear inequalities, I can use Autograph in the classroom as I often do but I am always keen to show them resources they can use at home.

The Desmos graphing calculator handles inequalities very well, unlike many free graph plotters it is easy to plot lines of the form x=k. Click on this image to see these inequalities on the Desmos calculator. See also this post on Mathematics for Students.

Desmos Inequalities
Experiment with these inequalities on the Desmos graphing calculator.

The Holt Online graphing calculator can deal with inequalities (though it cannot plot line of the form x=k) and gives a very clear display.

To enter an inequality, click on the equals sign, then select the required choice:

Up to four inequalities can be entered.

I am puzzled by WolframAlpha currently as I thought this would be an obvious resource to use. The inequalities examples here are fine,  however I don’t think this inequality plot for x+y<5 would help my students much!

4 comments on “Graphing Inequalities

  1. Can’t beat Autograph though. I have just taught year 9 that the standard is to shade the area you don’t want (the default in Autograph, though it can be changed) … I am a bit wary of confusing them with Desmos, which does it the other way round, and so far as I can see, cannot be changed.

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    • David I agree that Autograph is excellent for inequalities (though Autograph costs money and Desmos doesn’t!). Certainly when showing several inequalities on one diagram then shading the unwanted region is much clearer. You are correct, Desmos does not have that option (at the moment). I always suggest to students that they note with any answers which region they have shaded.

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