Answer
$\dfrac{-\sqrt{3}}{2}$
Work Step by Step
Rationalize the denominator by multiplying $\sqrt{3}$ to both the numerator and the denominator to have:
$=\dfrac{-3}{\sqrt{12}} \cdot \dfrac{\sqrt{3}}{\sqrt{3}}
\\=\dfrac{-3\sqrt{3}}{\sqrt{36}}
\\=\dfrac{-3\sqrt3}{6}$
Cancel the common factor $3$ to have:
$=\dfrac{-\sqrt{3}}{2}$
