Squeeze theorem

The Twelfth Doctor once used the squeeze theorem to prove that $$\lim_{\theta\to 0} \frac {sin \theta} {\theta} = 1$$. During the demonstration, the Doctor used mathematical concepts such as sin, cos, tan, inequalities and limit. (TV: The Pilot)

Behind the scenes
Although the name "squeeze theorem" wasn't used, and the demonstration wasn't explained by the Doctor, it is a faily basic calculus theorem, and can be recognised by the viewers.