Adding or subtracting radicals is the same concept as that of adding or subtracting similar, or "like", terms. The index and the values under the radical (the radicands) must be the SAME (creating "like radicals") before you can add or subtract the radical expressions.

Adding and subtracting radicals: For radicals having the same index and the same values under the radical (the radicands), add (or subtract) the values in front of the radicals and keep the radical. 



REMEMBER: Always simplify first! When the radicals in an addition or subtraction problem are different, be sure to check to see if the radicals can be simplified. It may be the case that when the radicals are simplified, they will become "like" radicals, making it possible for them to be added or subtracted. 
