If you don't have a formula editor, you can use office Setup to install it.

Start Wood, right-click the toolbar, select the "Custom" option and tick the "Custom" box, click the "Command" tab, select the "Insert" option in the "Category" column, find the "Formula Editor" option in the "Command" column on the right, hold down the left key and drag the toolbar and close the box. Insert the OFFICE installation CD, press the "Formula Editor" button in the toolbar, and then press the formula editor line after prompting (execute the "Insert-Image" command). For reference.