Question 469802
As long as the irrational number is EXACTLY the same, it's like with variables: 19x-6x=13x.  If you have 19 "square root of 2"s, and you subtract 6 "square root of 2"s, you still have 13 "square root of 2"s: {{{ 19sqrt(2)-6sqrt(2)=13sqrt(2) }}}



If it wasn't the same irrational number, like {{{ 19sqrt(2)-6sqrt(3) }}}, then they're not like terms.  That would be like 19x-6y, which you can't combine.  However, some radicals can be simplified so that the irrational numbers DO match.  It doesn't sound like you're at that point just yet, so I won't go into detail.  Just remember: adding and subtracting radicals (irrational numbers) is just like adding and subtracting variables: you can combine them if they're like terms.