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That is, unless the configuration for MathJax which this site uses is not change. A bit more details on this can be found here: Poll for MathJax macros that should be automatically loaded (Mathematics Meta).

That is, unless the configuration for MathJax which this site uses is changed in such way that this is loaded automatically. A bit more details on this can be found here: Poll for MathJax macros that should be automatically loaded (Mathematics Meta).

It is a bad practice to use MathJax for formatting and not for Mathematics. So it is not good to use MathJax to achieve strikethrough. (MathJax also gives information which part is mathematical formula and which part is text. This information is used, for example, by screen readers, by search engines that specialize in search for mathematical formulas, etc. In general, it is better to avoid mixing between syntax and semantics, between formatting and marking type of text - in this case distinguishing between mathematics and normal text.)

It is, in my opinion, a bad practice to use MathJax for formatting and not for Mathematics. So it is not good to use MathJax to achieve strikethrough. (MathJax also gives information which part is mathematical formula and which part is text. This information is used, for example, by screen readers, by search engines that specialize in search for mathematical formulas, etc. In general, it is better to avoid mixing between syntax and semantics, between formatting and marking type of text - in this case distinguishing between mathematics and normal text.)

See also: How to strike text? and Does markdown have a way to express strikeout? on Meta Stack Exchange. (As mentioned there in chat you can use ---this--- to achieve similar effect.

In the current revision of the post you linked, the \cancel command does not work for two reasons. Firstly, you cannot expect MathJax command work outside MathJax environment. (I.e., it has to be marked by dollars or some other way which denotes MathJax.)

See also: How to strike text? and Does markdown have a way to express strikeout? on Meta Stack Exchange. (As mentioned there in chat you can use ---this--- to achieve similar effect.)

In the current revision (at the time I posted this answer) of the post you linked, the \cancel command does not work for two reasons. Firstly, you cannot expect MathJax command work outside MathJax environment. (I.e., it has to be marked by dollars or some other way which denotes MathJax.)