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.

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!

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.

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.

In Decision 1 David’s suggestion is the preferred method

It is indeed – and the logical choice when one has several constraints.

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.

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.