sqrt((sqrt(3+1)^2+(3-1)^2)
Your brackets are unbalanced but this is what I have interpreted.
$$\\\sqrt{\sqrt{3+1}^2+(3-1)^2}\\\\ =\sqrt{\sqrt{4}^2\;\;+\;\;(2)^2}\\\\ =\sqrt{4+4}\\\\ =\sqrt{4*2}\\\\ =2\sqrt{2}\\\\$$