$\left\{1,2,3,4\right\}$

$\left\{2,3,4\right\}$

$\left\{2,4\right\}$

$\left\{4\right\}$

充分不必要条件

必要不充分条件

充要条件

既不充分也不必要条件

$f\left(x\right)=\frac{x}{1-\left|x\right|}$

$f\left(x\right)=\frac{x}{\left|x\right|-1}$

$f\left(x\right)=\frac{\left|x\right|}{1-x^2}$

$f\left(x\right)=\frac{\left|x\right|}{x^2-1}$

若 $m\text{//}\alpha ,n\subset \alpha$，则 $m\text{//}n$

若 $m\perp \alpha ,m\perp \beta$，则 $\alpha \perp \beta$

若 $m\text{//}\alpha ,m\perp \beta$，则 $\alpha \perp \beta$

若 $m\subset \alpha ,\alpha \perp \beta$，则 $m\perp \beta$

若 $X\sim N\left(\mu ,{\sigma }^2\right)$，则 $P(X\le \mu -\sigma )=P(X\ge \mu +\sigma )$

若 $X\sim N\left(1,2^2\right)$， $Y\sim N\left(2,2^2\right)$，则 $P(X<1)<P(Y<2)$

$\left|r\right|$越接近 $1$，相关性越强

$\left|r\right|$越接近 $0$，相关性越弱