How do you simplify #sqrt(1+9x^4)#?
That's about as simple is it can be.
You can factor the radicand as
but there are no square factors to allow simplification.
If the radicand of a square root has a square factor, then you can move that outside the square root.
With variables you have to be a little more careful, but you can say:
In the case of
We can factor the radicand to get:
but I would not call that simpler.