Hi there,

Does anyone know how to use Tex notation to cross-out parts of a expression? The idea is that I wil use moodle to teach logic to people who, most of the time, don´t understand math. So, if I have something like:

$$ \frac{20! 6!}{18! 5!} = \frac{20.19.18!.6.5!}{18! 5!} = 20.19.6 = 2280$$

It is obvious that 18! and 5! are both canceled out, but several people are not able to see that and I need to show on screen that the numerators and denominators are being crossed out. I tried doing that in different ways, but the only option that showed some promisse was using "\not" before what I wanted to cross out. Like that:

$$ \frac{20! 6!}{18! 5!} = \frac{20.19.\not18!.6.\not5!}{\not18! \not5!} = 20.19.6 = 2280$$

But, as you can see, for 18! and 5! just 1 and 5 are crossed out and I would like something like ~~18!~~ and ~~5!~~. The crossing out of just the first element would confuse the students, for sure. As it seems, \not would only work for unitary stuff, such as crossing out variables like on (and remember that my students are, mostly, completely dumb about math):

$$ \frac{2x}{x} = \frac{2\not x}{\not x}=2$$

Anyone know an alternative to cross out?