this piece of latex can be rendered correctly on math.stackexchange.com
$\operatorname{var}[\boldsymbol{\mathrm{AD}}+\mathbf{b}] = \boldsymbol{\mathrm{A}} \operatorname{var}[\boldsymbol{\mathrm{D}}]\boldsymbol{\mathrm{A}}^T$
gives this figure
how to render it correctly on tex.stackexchange.com?