UK TeX FAQ -- question 168

### Cancelling terms in maths expressions

A technique used when explaining the behaviour of expressions or equations (often for pedagogical purposes). The cancel package provides several variants of cancellation marks ("`\`", "`/`" and "`X`"), and a means of cancelling 'to' a particular value.

Documentation of cancel is in the package file.

`cancel.sty`
  macros/latex/contrib/other/misc/cancel.sty