Lagrange's theorem
$\textbf{Lagrange's theorem}$
Let $G$ be a finite group, then the order of every subgroup $H$ of $G$ divides the order of $G$.
𝐋𝐚𝐠𝐫𝐚𝐧𝐠𝐞’𝐬 𝐭𝐡𝐞𝐨𝐫𝐞𝐦
Let 𝐺 be a finite group, then the order of every subgroup 𝐻 of 𝐺 divides the order of 𝐺.