{\displaystyle [\sigma _{a},\sigma _{b}]+\{\sigma _{a},\sigma _{b}\}=(\sigma _{a}\sigma _{b}-\sigma _{b}\sigma _{a})+(\sigma _{a}\sigma _{b}+\sigma _{b}\sigma _{a})=2i\varepsilon _{abc}\sigma _{c}+2\delta _{ab}I=2\sigma _{a}\sigma _{b}}