Enter any matrix as a solution.

Click on the square root button $($if necessary, click on

the $3$ vertical dots first$)$

Click on "Switch View to Advanced"

Type the following:

Click "Insert Equation.

$\backslash$begin$\{$bmatrix$\}$ and end $\}\backslash$backslash $\{$ bmatrix$\}$ tells the compiler that

we're making a matrix with square brackets.

& separates the entry in each row.

$\frac{\frac{?}{?}}{\frac{?}{?}}\frac{?}{?}$ means next row.