Let's simplify the expression step by step:

√(13+√105) = √(13+√(5*21)) = √(13+√5√21) = √(13+√5√3√7) = √(13+√15√7)

√(13-√105) = √(13-√(5*21)) = √(13-√5√21) = √(13-√5√3√7) = √(13-√15√7)

Now, let's add both results:
√(13+√15√7) + √(13-√15√7)

Let's square the result:
(√(13+√15√7) + √(13-√15√7))^2 = 13 + √15√7 + √15√7 + 13
= 26 + 2√15√7
= 26 + 2√(157)
= 26 + 2√105
= 26 + 2√(521)
= 26 + 2√5√21
= 26 + 2√5√3√7
= 26 + 2√15√7

So, the final simplified expression is (26 + 2√15√7)^2.