a ) \(\dfrac{\left(x-3\right)^2}{3}-\dfrac{\left(2x-1\right)^2}{12}\le x\)
\(\Leftrightarrow4\left(x-3\right)^2-\left(2x-1\right)^2\le12x\)
\(\Leftrightarrow4\left(x^2-6x+9\right)-\left(4x^2-4x+1\right)-12x\le0\)
\(\Leftrightarrow4x^2-24x+36-4x^2+4x-1-12x\le0\)
\(\Leftrightarrow-36x\le-35\)
\(\Leftrightarrow x\ge\dfrac{35}{36}\)
Vậy bất phương trình có nghiệm \(x\ge\dfrac{35}{36}\).
b ) \(2+\dfrac{3\left(x+1\right)}{3}< 3-\dfrac{x-1}{4}\)
\(\Leftrightarrow2+x+1< 3-\dfrac{x-1}{4}\)
\(\Leftrightarrow x+3< 3-\dfrac{x-1}{4}\)
\(\Leftrightarrow4\left(x+3\right)< 12-x+1\)
\(\Leftrightarrow4x+12+x< 13\)
\(\Leftrightarrow5x< 13-12\)
\(\Leftrightarrow5x< 1\)
\(\Leftrightarrow x< \dfrac{1}{5}\)
Vậy bất phương trình có nghiệm \(x< \dfrac{1}{5}\)