You can apply protection to any cell containing a formula without affecting
the cell(s) it applies to. EG if A1 contains =B1+C1, protecting A1 won't
affect B1 or C1.
An easy way to protect all your formula is to hit 'Edit' on the toolbar, 'Go
To' > Click 'Special', check 'Formulas' > OK
This highlights all your formulas. Right click in one of them, 'Format
Cells' > 'Protection' > OK
Protect the worksheet by 'Tools' > 'Protection' > Protect Sheet', Password
it if you want to, > OK
Note that Protection is not Security, Excel worksheet passwords are very
easily cracked by anyone with a little knowledge and the will to do so,
Regards,
Alan.