Similar to 余弦定理

Proof that 22/7 exceeds π

Proof that π is irrational

Euler's formula

Interesting number paradox

Open mapping theorem (complex analysis)

Rank–nullity theorem

Gauss's lemma (number theory)

Carathéodory's theorem (convex hull)

Leibniz formula for determinants

Locally connected space

Coupon collector's problem

Casey's theorem

Kőnig's lemma

Primitive Pythagorean triple

Cauchy's mean value theorem

Mean value theorem (divided differences)

Schiffler point

Shannon's source coding theorem

Noisy-channel coding theorem

Jordan's lemma

Sylvester–Gallai theorem

Analyticity of holomorphic functions

Linear independence

Diagonal lemma

Thales's theorem

Monotone convergence theorem

Intermediate value theorem

Parallelogram law