Cannot render LaTeX in VScode Jupyter Notebook

I have homework in VScode Jupyter Notebook but I get a lot of ParseError in it when displaying the LateX. The error is

ParseError: kaTeX parse error:Undefined control sequence.

for example one of the Markdown cells is

$\newcommand{\vect}[1]{{\mathbf{\boldsymbol{{#1}}}}}$
This is the vector $\vect{x}$.

and the jupyter cannot render it I guess? (I am not very familar with LateX) and will get the following error parse error