Answer
The domain of $$ D=\{s\in R; s\geq 0\}.$$
Work Step by Step
Given $$ r(s)=e^si+\sqrt s j+\cos s k $$
We know that $\sqrt s $ is not defined for negative values of $ s $, whereas $e^s$ and $\cos s$ are defined for all numbers. Thus the domain of $$ D=\{s\in R; s\geq 0\}.$$
