I have two functions that are totally equivalent $\displaystyle sqrt(1+t^3)-1$ and $\displaystyle t^3/(sqrt(1+t^3)+1)$... so which is more precise when $\displaystyle t=10^-^6$?

Now I believe that the second one is more accurate and if u plug it into a calculator it has more decimal values in its approximation. But why is it more precise?