R
array?Size: a a a
А
\left(\begin{array}{cc}
\qty (1 + \cos(\bf{k \cdot a_3})) \hat{\sigma_2} + \sin(\bf{k \cdot a_3}) \hat{\sigma_1} & \hat{O} \\
\multirow{2}{*}{$\hat{O}$} & - \qty (\cos(\bf{k \cdot a_1})+ \cos(\bf{k \cdot a_2})) \hat{\sigma_2}
\\ &- \qty (\sin(\bf{k \cdot a_1}) + \sin(\bf{k \cdot a_2})) \hat{\sigma_{1}}
\end{array} \right)ও
ও
А
А

ও

ও

NM
NM
R
\mathbin или \mathrelКК