How do I make matrices of various sizes?

[me2youall]

I wish to make a larger matrix but I cannot figure out how to add collums. I
understand that if I hit enter then I get an additional row, but I cannot
figure out how to make more columns.

 

[Jay Freedman]

I wish to make a larger matrix but I cannot figure out how to add collums. I
understand that if I hit enter then I get an additional row, but I cannot
figure out how to make more columns.

If you only need one or two more columns, right-click any entry in the rightmost
column and choose Insert > Insert Column After, repeating as often as needed.

If you need many more columns, this gets tedious. Instead, on the right-click
menu choose Linear. There will be a black square followed by an expression like

(1&2@3&4@5&6)

Put the cursor immediately to the left of the first @ sign and insert more &
signs, one for each new column. Then right-click again and choose Professional.

 

[JoAnn Paules]

Table - Insert - Column