The formula only appears in the formula bar while the results appear in the workbook cells in Excel Online. But you can do a screen capture or copy and paste the formulas to an application like Notepad and then print them.
If you have Excel desktop application, you can use the Open in Excel button to open the workbook and show and print formulas.
Click Open in Excel and show and print formulas.
For news about the latest Excel Online updates, visit the Microsoft Excel blog.