1) \(ĐKXĐ:5+x^2\ge0\left(đúng\forall x\right)\)
Vậy \(x\in R\)
2)ĐKXĐ: \(\dfrac{5}{x+4}\ge0\Leftrightarrow x+4>0\Leftrightarrow x>-4\)
3) ĐKXĐ: \(x^2-2x+1\ge0\Leftrightarrow\left(x-1\right)^2\ge0\left(đúng\forall x\right)\)
Vậy \(x\in R\)
4)ĐKXĐ: \(-x^2-2x-1\ge0\)
Mà \(-x^2-2x-1=-\left(x+1\right)^2\le0\forall x\)
Vậy \(x\in\left\{\varnothing\right\}\)