I. 2) radical sign here refers to the square root signs, in general to nth root
1) x=3 is obviously a solution. Else
(a) x>3.
Then \sqrt{3x}<x \Rightarrow \sqrt{x + 2 \sqrt{3x}}<x
Successive use of this (starting from the right) gives you LHS<x
(b)x<3
Then \sqrt{3x}>x \Rightarrow \sqrt{x + 2 \sqrt{3x}}>x
Following the same procedure as above we get LHS>x
Thus x=3 is the unique solution