\(a,ĐK:1-4x\ge0\Leftrightarrow x\le\dfrac{1}{4}\\ b,ĐK:\dfrac{x-3}{-6}\ge0\Leftrightarrow x-3\le0\left(-6< 0\right)\Leftrightarrow x\le3\\ c,ĐK:\dfrac{4}{x+3}\ge0\Leftrightarrow x+3>0\left(4>0;x+3\ne0\right)\Leftrightarrow x>-3\\ d,ĐK:\dfrac{-5}{x^2+6}\ge0\Leftrightarrow x\in\varnothing\left(-5< 0;x^2+6>0\right)\)
\(e,ĐK:\dfrac{2+x}{5-x}\ge0\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}2+x\ge0\\5-x\ge0\end{matrix}\right.\\\left\{{}\begin{matrix}2+x\le0\\5-x\le0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x\ge-2\\x\le5\end{matrix}\right.\\\left\{{}\begin{matrix}x\le-2\\x\ge5\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}-2\le x\le5\\x\in\varnothing\end{matrix}\right.\Leftrightarrow-2\le x\le5\)
