- Hướng dẫn giải

Đáp án là A.

• Ta có $\underset{x\to -\infty }{\lim }\frac{\sqrt{x^2-x}-\sqrt{4x^2+1}}{2x+3}=\underset{x\to -\infty }{\lim }\frac{\left|x\right|\left(\sqrt{1-\frac{1}{x}}-\sqrt{4+\frac{1}{x^2}}\right)}{x\left(2+\frac{3}{x}\right)}$$=\underset{x\to -\infty }{\lim }\frac{-\left(\sqrt{1-\frac{1}{x}}-\sqrt{4+\frac{1}{x^2}}\right)}{\left(2+\frac{3}{x}\right)}$$=\frac{1}{2}$