x = ∑ n = 0 ∞ 1 n ! = lim n → ∞ 1 0 ! + 1 1 ! + 1 2 ! + ⋯ + 1 n ! {\displaystyle x=\sum _{n=0}^{\infty }{\frac {1}{n!}}=\lim _{n\to \infty }{{\frac {1}{0!}}+{\frac {1}{1!}}+{\frac {1}{2!}}+\cdots +{\frac {1}{n!}}}}
a ∉ R {\displaystyle a\not \in \mathbb {R} }
a ≠ B {\displaystyle a\not =B}
x = { x | x 2 < 1 } {\displaystyle x=\left\{x\left|{\frac {x}{2}}<1\right\}\right.}
( n r ) {\displaystyle {\binom {n}{r}}}
