连乘
prod_{i=1}^n
[prod_{i=1}^n
]
分数
frac{a}{b}
[frac{a}{b}
]
组合数
binom{n}{r}= binom{n}{n-r}=C^n_r=C^n_{n-r}
[ binom{n}{r} = binom{n}{n-r} = C^n_r = C^n_{n-r}
]
(egin{align*}x^n = sumlimits_{k=1}^nleft{egin{matrix}n\kend{matrix} ight}x^underline kend{align*})