1. In any cell, type -1.
2. Select the cell and press Ctrl+C to copy.
3. Select the range to be multiplied by -1.
4. Press Shift+F10 or right-click, and then select Paste Special from the shortcut menu.
5. Select the Multiply option button, and then click OK.
Note: *-1 and parentheses are added in any cell with a formula.
Screenshot // Multiplying a Range by -1 in One Operation