$D=\mathbb{R}\backslash \left\{ 0 \right\}$.

Ta có $y=\frac{3{{x}^{2}}}{{{x}^{2}}-x}=\frac{3{{x}^{2}}}{x\left( x-1 \right)}=\frac{3x}{x-1}$.

Khi đó $\underset{x\to {{1}^{-}}}{\mathop{\lim }}\,y=\underset{x\to {{1}^{-}}}{\mathop{\lim }}\,\frac{3x}{x-1}=-\infty ;\underset{x\to {{1}^{+}}}{\mathop{\lim }}\,y=+\infty $

$\Rightarrow TCD:x=1$.

$\underset{x\to +\infty }{\mathop{\lim }}\,y=\underset{x\to -\infty }{\mathop{\lim }}\,y=3\Rightarrow TCN:y=3$