7. (2+sqrt(6))(2-sqrt(6)) = 4 - 6 = -2.

2*sqrt(3)*sqrt(12) = sqrt(3)*sqrt(3*4) = sqrt(3)*sqrt(3)*2 = 3*2 = 6

So column B is the greater

The others are similar to column B in this question, the numbers under

the root signs are reduced to their prime factorisations, the factors that

appear twice are brought out from under the root sign, and whatever can

be cancelled is cancelled.

RonL