R,[−1,1]\mathbb{R},[-1,1]R,[−1,1]
R−{(2n+1)π2,n∈Z},R\mathbb{R}-\left\{(2 n+1) \frac{\pi}{2}, n \in \mathbb{Z}\right\}, \mathbb{R}R−{(2n+1)2π,n∈Z},R
R,R\mathbb{R}, \mathbb{R}R,R
R−{nπ,n∈Z},R\mathbb{R}-\{\mathrm{n} \pi, \mathrm{n} \in \mathbb{Z}\}, \mathbb{R}R−{nπ,n∈Z},R