http://stephenteacher.tiddlyspot.com/#Unit%2011%20M1%20Solution%3AJoint%203
As you can see on a mobile display the equations over run the bounds of the tiddler when viewed in portrait.
Cheers.
It seems that as the equations are in a bordeless table to keep alignment (I don't think katex supports align environments but I could be wrong) I can just use the solution to the long tables problem.
Though the question is still valid for non tabled katex equations.
Cheers