Sum of Radicals
Two radicals can be added only if their indexes and radicands are equal.
For example, these two radicals cannot be added:
[tex]\sqrt[]{a}+\sqrt[3]{a}[/tex]Because they don't have the same index even though they have the same radicand.
We have the sum of:
[tex]2\sqrt[]{6}+6\sqrt[]{6}[/tex]The radicands and indexes are exactly equal, so we can add their coefficients as follows:
[tex]2\sqrt[]{6}+6\sqrt[]{6}=8\sqrt[]{6}[/tex]