Answer
$(-\infty,-1)\cup[1,\infty)$
Work Step by Step
Step 1. The domain requirement for the given function $f(x)=\sqrt {\frac{2x}{x+1}-1}$ is that $\frac{2x}{x+1}-1\geq0$
Step 2. From the above inequality, we have $\frac{2x-x-1}{x+1}\geq0$, $\frac{x-1}{x+1}\geq0$, and the boundary points are $x=-1,1$
Step 3. Using test points to examine signs of the left side across the boundary points, we have
$...(+)...(-1)...(-)...(1)...(+)...$
Thus the solutions are $x\lt-1$ or $x\geq1$
Step 4. We can express the solutions in interval notation as $(-\infty,-1)\cup[1,\infty)$
