Here is a tutorial to lock or hide only the formula cells in an Excel workbook. You can also lock formulas in all worksheets in a workbook.

Protecting cells in your Microsoft Office Excel 2010 spreadsheet is a good idea because it enables other people to view the spreadsheet but prevents them from modifying your data and formulas ...

You may end up with an Excel sheet with lots of cells with a leading apostrophe, which tells Excel to interpret the cell content as a text. It may not be very pleasant and makes all the other formulas ...