https://s0.wp.com/latex.php?latex=%5Cdisplaystyle++%7B%5Crm+Var%7D_t%28X%29%5Cle%7B%5Cmathbb+E%7D%5BY_0-Y_t%5D%2B%7B%5Cmathbb+E%7D%5BZ_0-Z_t%5D%2C+&bg=ffffff&fg=000000&s=0&c=20201002